Optical compensating sheet, polarizing plate, and liquid-crystal display

ABSTRACT

An optical compensatory sheet comprises a cellulose acetate film. The film contains 100 weight parts of cellulose acetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20 weight parts of an aromatic compound having at least two aromatic rings. The cellulose acetate film has an Re retardation value measured at 550 nm (Re550) in the range of 0 to 200 nm and an Rth retardation value measured at 550 nm (Rth550) in the range of 70 to 400 nm. The cellulose acetate film further has a thickness in the range of 10 to 70 μm. The optical compensatory sheet is used in a liquid crystal display.

FIELD OF INVENTION

[0001] The present invention relates to an optical compensatory sheet, apolarizing plate and a liquid crystal display using the same.

BACKGROUND OF INVENTION

[0002] A cellulose acetate film is used in various photographic oroptical elements because it is tough and has enough flame retardantproperties. The cellulose acetate film is a representative photographicsupport. Further, the film is also used in a liquid crystal display. Thecellulose acetate film has a high optical isotropy (giving relativelylow retardation) compared with other polymer films. Accordingly, anoptical isotropic film such as a protective film of a polarizing plateusually comprises the cellulose acetate film.

[0003] On the other hand, an optical compensatory sheet (phase retarder)in a liquid crystal display must have optical anisotropy (must give highretardation). Accordingly, a film of synthetic polymer (such aspolycarbonate or polysulfone) giving high retardation is normally usedas the compensatory sheet. In practice, the film of synthetic polymer isstretched to prepare a stretched birefringent film for the opticalcompensatory sheet.

[0004] As described above, generally in the technical field of opticalelements, the synthetic polymer film is used as the element that musthave optical anisotropy (must give high retardation), while thecellulose acetate film is used as the element that must have opticalisotropy (must give low retardation).

[0005] In contrast, European Patent No. 0911656A2 discloses a celluloseacetate film giving such high retardation that it can be used as anoptical anisotropic element. A liquid crystal display can give an imageof high quality where the cellulose acetate film is provided between apolarizing plate and a liquid crystal cell.

[0006] In place of the stretched birefringent film, an opticalcompensatory sheet comprising a transparent support and a thereonprovided optically anisotropic layer comprising discotic molecules hasbeen proposed. The optically anisotropic layer is formed through thesteps of aligning the discotic molecules and then fixing the alignment.The discotic molecules give large birefringence and have variousalignment forms, and accordingly an optical compensatory sheet obtainedfrom the discotic molecules has a specific optical characteristic thatcannot be obtained from the conventional stretched birefringent film.The optical compensatory sheet comprising discotic molecules isdescribed in Japanese Patent Provisional Publication No. 6(1994)-214116,U.S. Pat. Nos. 5,583,679, 5,646,703 and German Patent Publication No.3,911,620A1.

[0007] The optical compensatory sheet is also used in a λ/4 plate, whichis widely used in an anti-reflection film or a liquid crystal display.However, in spite of the name of λ/4, most λ/4 plates give λ/4 atparticular wavelengths.

[0008] Japanese Patent Provisional Publication Nos. 5(1993)-27118 and5(1993)-27119 disclose a λ/4 plate in which a birefringent film givinghigh retardation and another birefringent film giving low retardationare laminated so that their optical axes may be perpendicularly crossed.If the retardation difference of those films is kept λ/4 in the wholevisible wavelength region, the λ/4 plate theoretically gives λ/4 in thewhole visible wavelength region.

[0009] Japanese Patent Provisional Publication No. 10(1998)-68816discloses a λ/4 plate giving λ/4 in a wide wavelength region. Thedisclosed λ/4 plate comprises laminated two films made of the samepolymer, and one of the films gives λ/4 and the other gives λ/2 at thesame wavelength. Japanese Patent Provisional Publication No.10(1998)-90521 also describes another wide-ranging λ/4 plate comprisinglaminated two polymer films. As the polymer film used in the abovedisclosed λ/4 plates, a stretched film of synthetic polymer such aspolycarbonate is used.

[0010] A liquid crystal display (hereinafter often referred to as LCD)is widely employed instead of CRT (cathode ray tube) because of itssmall thickness, lightweight, and low power consumption. The liquidcrystal display generally comprises a pair of polarizing plates and aliquid crystal cell provided between them. The liquid crystal cellcomprises a pair of substrates, rod-like liquid crystal molecules and anelectrode layer. The rod-like liquid crystal molecules are providedbetween the substrates, and the electrode layer has a function ofapplying a voltage to the rod-like liquid crystal molecules. On eachsubstrate, an orientation layer is provided to align the rod-like liquidcrystal molecules. Each polarizing plate comprises a pair of transparentprotective films and a polarizing membrane provided between them.

[0011] In the liquid crystal display, an optical compensatory sheet(phase retarder) is often provided between the liquid crystal cell andthe polarizing plate, to prevent the displayed image from undesirablecoloring. The layered composition of the polarizing plate (or polarizingmembrane) and the optical compensatory sheet serves as an ellipticallypolarizing plate. The optical compensatory sheet also often enlarges aviewing angle of the liquid crystal cell. As the optical compensatorysheet, a stretched birefringent polymer film has been conventionallyused.

[0012] In a TFT (thin film transistor) liquid crystal display of TN(twisted nematic) mode (which is widely and mainly used), the opticalcompensatory sheet is provided between the liquid crystal cell and thepolarizing plate (in the manner described in Japanese Patent ProvisionalPublication No. 8(1996)-50206) to ensure an image of high quality.However, that liquid crystal display is often made relatively thick.

[0013] Japanese Patent Provisional Publication No. 1(1989)-68940discloses another liquid crystal display. In the liquid crystal display,the optical compensatory sheet is provided on one surface of thepolarizing membrane, and on the other surface an elliptically polarizingplate having a protective film is provided. That liquid crystal displaycan be made relatively thin, and can give an image with high contrastwhen seen frontally. However, the optical compensatory sheet in thedisplay is often deformed (for example, by heat) to cause phaseretardation. If so, when the display gives a black image, thetransmittance at the peripheral part of the screen so increases that thedisplayed image is framed with leaked light. Thus, the liquid crystaldisplay has insufficient durability.

[0014] In order to solve the above problem, Japanese Patent ProvisionalPublication No. 7(1995)-191217 and European Patent No. 0911656A2disclose another liquid crystal display. In the disclosed display, anoptically anisotropic layer comprising a discotic compound is providedon a transparent support to form an optical compensatory sheet servingas the protective film of the polarizing plate. That liquid crystaldisplay can be made relatively thin, and has improved durability.

[0015] U.S. Pat. Nos. 4,583,825 and 5,410,422 disclose a liquid crystaldisplay comprising a liquid crystal cell of bend alignment mode in whichrod-like liquid crystal molecules in upper part and ones in lower partare aligned essentially in reverse (symmetrically). Since rod-likeliquid crystal molecules in upper part and ones in lower part aresymmetrically aligned, the liquid crystal cell of bend alignment modehas self-optical compensatory function. Therefore, this mode is referredto as OCB (optically compensatory bend) mode. The liquid crystal displayof bend alignment mode has an advantage of responding rapidly.

[0016] The liquid crystal display of bend alignment mode respondsrapidly, and gives a clear image within a wide viewing angle, ascompared with a generally used display (e.g., a display of TN mode orSTN mode). However, in order to take the place of CRT, the display ofbend alignment mode must be further improved.

[0017] To improve the display of bend alignment mode, the opticalcompensatory sheet (which is generally used to improve a conventionaldisplay) may be used. However, a conventional compensatory sheet ofstretched birefringent film cannot fully compensate the display of bendalignment mode.

[0018] As described above, an optical compensatory sheet comprising atransparent support and a thereon provided optically anisotropic layercomprising discotic molecules has been proposed in place of thestretched birefringent film. In fact, Japanese Patent ProvisionalPublication No. 9(1997)-197397 (corresponding to U.S. Pat. No.5,805,253) and International Patent WO96/37804 (corresponding toEuropean Patent Application No. 0783128A) disclose a liquid crystaldisplay of bend alignment mode equipped with the optical compensatorysheet comprising discotic molecules. The compensatory sheet comprisingdiscotic molecules remarkably improves the viewing angle of bendalignment mode display.

[0019] However, according to Japanese Patent Provisional Publication No.11(1999)-316378, light at a particular wavelength often leaks to colorthe displayed image undesirably if the optical compensatory sheetcomprising discotic molecules is used in the liquid crystal display ofbend alignment mode. The publication reports that this undesiredcoloring is due to wavelength dependence of transmittance of theelliptically polarizing plate (layered composition of the polarizingdevice and the optical compensatory sheet).

[0020] In the publication, to avoid the undesired coloring, thepolarizing membrane and the optical compensatory sheet are placed sothat the average direction obtained by projecting normal of the discplane of the discotic molecule onto the support may be essentially atthe angle of 45° to the polarizing axis in the plane of polarizingmembrane. The thus-placed optical compensatory sheet fully compensatesthe liquid crystal cell of bend alignment.

SUMMARY OF INVENTION

[0021] The inventors have found that, in the case where a polarizingplate in which an optical compensatory sheet (a cellulose acetate filmor a cellulose acetate film having an optically anisotropic layerprovided thereon) works as a protective film is attached on a largedisplay panel (17 inches or more), the sheet cannot be fully preventedfrom deforming by heat to increase the transmittance at the peripheralpart of the screen (consequently, to framewise leak light). Accordingly,it is necessary for the optical compensatory sheet not only to opticallycompensate a liquid crystal cell but also to have excellent durabilityagainst fluctuation of working conditions such as heat and moisture.

[0022] In the case where an optical compensatory sheet serves as a λ/4plate, two polymer films are normally laminated to give λ/4 in a widewavelength region. The films, however, must be carefully placed so thatthe angle between them may be strictly controlled.

[0023] Although a λ/4 plate consisting of one polymer film has beenproposed, it hardly gives λ/4 in a wide wavelength region. Further, evenif such single-film λ/4 plate is installed in a liquid crystal display,the viewing angle property is not so much improved as expected. On theother hand, if the single-film λ/4 plate is installed in a liquidcrystal display of reflection type, the displayed image has contrast notinferior to an image given by a display equipped with the aforementionedλ/4 plate consisting of laminated films. However, when such display ofreflection type is used in a mobile terminal device (particularly, whenused as a large display of the device, for which displays of reflectiontype are generally used), it does not have enough durability againstheat. In fact, the film of λ/4 plate is distorted with heat generated byelements of the display (e.g., backlight), and accordingly theretardation value becomes uneven and the slow axis changes its directionin the plane of the film. As a result, the transmittance at theperipheral part of the liquid crystal cell increases when the displaygives a black image, and consequently the displayed image is framed withleaked light.

[0024] A polarizing plate used in a liquid crystal display comprises apair of transparent protective films and a polarizing membrane providedbetween them. Therefore, if the aforementioned optical compensatorysheet is laminated on the polarizing membrane to form an ellipticallypolarizing plate, the compensatory sheet serves as the protective film(on one side) of the polarizing membrane. The thus-formed ellipticallypolarizing plate has a layered structure in which the transparentprotective film, the polarizing membrane and the optical compensatorysheet are piled up in this order. Since the compensatory sheet replacesone protective film of the polarizing plate, the display can be madethinner and lighter. Further, in preparation of that display, the stepof assembling the reduced element is omitted and hence troubles inassembling can be reduced.

[0025] In the case where a cellulose acetate film is used as thetransparent protective film, it is a problem that the cellulose acetatefilm has poor affinity to the polarizing membrane (normally, which ismade of polyvinyl alcohol). Actually, there is no adhesive that canstrongly bond them together. In Japanese Patent Provisional PublicationNo. 8(1996)-94838, the transparent protective film is saponified toimprove the affinity to the polarizing membrane. Through thesaponification of the transparent protective film, ester bonds ofcellulose acetate at the surface are partially hydrolyzed and reduced tohydroxyl groups of original cellulose. Since both cellulose andpolyvinyl alcohol are polymers having hydroxyl groups, they have goodaffinity. Accordingly, the polarizing membrane and the saponifiedtransparent protective film are easily combined.

[0026] The inventors have studied the polarizing plate comprising theprotective film, the polarizing membrane and the optical compensatorysheet composed of a saponified cellulose acetate film, piled up inorder. As a result, it is found that the optical functions of theoptical compensatory sheet are impaired as compared with that before thesaponification. Further, it is also found that the alkaline liquid usedfor the saponification yellows after the treatment. Furthermore, theinventers have found that there is room for improvement in the adhesionbetween the cellulose acetate film and the polarizing membrane.

[0027] As described above, a liquid crystal display is equipped with anoptical compensatory sheet comprising a cellulose acetate film or acellulose acetate film on which an optically anisotropic layer preparedfrom a liquid crystal compound is provided. In that display, thetransmittance at the peripheral part of the screen often increases. Inparticular, if the display has a large screen, the transmittance at theperipheral part remarkably increases.

[0028] On the other hand, a cellulose acetate film has poor affinity toother elements (e.g., polarizing membrane, orientation layer), andaccordingly the optical compensatory sheet should be improved indurability for practical use.

[0029] An object of the present invention is to provide an opticalcompensatory sheet that can optically compensate a liquid crystal cellwithout leaking light. The optical compensatory sheet aimed in theinvention comprises a cellulose acetate film or a cellulose acetate filmhaving an optically anisotropic layer provided thereon.

[0030] Another object of the invention is to provide an opticalcompensatory sheet (λ/4 plate) consisting of one cellulose acetate filmand giving λ/4 in a wide wavelength region without leaking light.

[0031] A further object of the invention is to provide an opticalcompensatory sheet that can optically compensate a liquid crystal celland that excels in adhesion onto a polarizing membrane.

[0032] A furthermore object of the invention is to provide an opticalcompensatory sheet whose optical functions are essentially not affectedby saponification.

[0033] A still further object of the invention is to provide anexcellent (elliptically) polarizing plate that does not leak light andthat excels in the adhesion. In the aimed polarizing plate, an opticalcompensatory sheet and a polarizing membrane are unified.

[0034] A still furthermore object of the invention is to provide acircularly polarizing plate giving circularly polarized light in a widewavelength region without leaking light and without causing troubles inthe adhesion. In the aimed polarizing plate, a λ/4 plate (opticalcompensatory sheet) and a polarizing membrane are unified.

[0035] The other object of the invention is to provide a liquid crystaldisplay (particularly, a display having a liquid crystal cell of OCBmode) that is optically compensated with an optical compensatory sheetwithout leaking light.

[0036] A liquid crystal cell is optically compensated with the opticalcompensatory sheet comprising a cellulose acetate film or a celluloseacetate film on which an optically anisotropic layer prepared from aliquid crystal compound is provided. According to the inventors' study,if the cellulose acetate film used for the compensatory sheet has athickness in the range of 10 to 70 μm, the liquid crystal display isprevented from leaking light. The relation between the thickness of thecellulose acetate film and the leakage of light is described after.

[0037] The present invention provides an optical compensatory sheetcomprising a cellulose acetate film which contains 100 weight parts ofcellulose acetate having an acetic acid content of 59.0 to 61.5%, and0.01 to 20 weight parts of an aromatic compound having at least twoaromatic rings, wherein the cellulose acetate film has an Re retardationvalue measured at 550 nm (Re550) in the range of 0 to 200 nm, an Rthretardation value measured at 550 nm (Rth550) in the range of 70 to 400nm, and a thickness in the range of 10 to 70 μm.

[0038] The retardation values in plane (Re) and in the thicknessdirection (Rth) of the film are defined by the following formulas (I)and (II), respectively.

Re=(nx−ny)×d  (I)

Rth=[{(nx+ny)/2}−nz]×d  (II)

[0039] In the formulas (I) and (II), nx is a refractive index along theslow axis (direction giving the maximum refractive index) in the planeof the film.

[0040] In the formulas (I) and (II), ny is a refractive index along thefast axis (direction giving the minimum refractive index) in the planeof the film.

[0041] In the formula (II), nz is a refractive index in the thicknessdirection of the film.

[0042] In the formulas (I) and (II), d is the thickness of the film interms of nm.

[0043] The invention also provides a polarizing plate which comprises apair of transparent protective films and a polarizing membrane providedbetween the films, one of said transparent protective films comprising acellulose acetate film which contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,wherein the cellulose acetate film has an Re retardation value measuredat 550 nm (Re550) in the range of 0 to 200 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm, and athickness in the range of 10 to 70 μm.

[0044] The invention further provides a liquid crystal displaycomprising a pair of polarizing plates and a liquid crystal cellprovided between the plates, wherein each of the polarizing platescomprises a pair of transparent protective films and a polarizingmembrane provided between the films, at least one of said transparentprotective films placed between the cell and the membranes comprising acellulose acetate film which contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,wherein the cellulose acetate film has an Re retardation value measuredat 550 nm (Re550) in the range of 0 to 200 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm, and athickness in the range of 10 to 70 μm.

[0045] The invention furthermore provides a circularly polarizing platewhich comprises an optical compensatory sheet and a linearly polarizingmembrane, said compensatory sheet and said linearly polarizing membranebeing so arranged that a slow axis in plane of the compensatory sheet isoriented essentially at an angle of 45° to a transmission axis of thelinearly polarizing plate, said optical compensatory sheet comprising acellulose acetate film which contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,wherein the cellulose acetate film has an Re retardation value measuredat 550 nm (Re550) in the range of 0 to 200 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm, a thickness inthe range of 10 to 70 μm, an Re retardation value measured at 450 nm(Re450) in the range of 100 to 125 nm, and an Re retardation valuemeasured at 590 nm (Re590) in the range of 120 to 160 nm, said Re450 andRe590 values satisfying the condition of Re590−Re450≧2 nm.

[0046] The invention still further provides a liquid crystal display ofa reflection type comprising a reflection board, a liquid crystal celland a polarizing membrane in this order, and a cellulose acetate filmbeing provided between said reflection board and said polarizingmembrane, wherein the cellulose acetate film contains 100 weight partsof cellulose acetate having an acetic acid content of 59.0 to 61.5% and0.01 to 20 weight parts of an aromatic compound having at least twoaromatic rings, said cellulose acetate film having an Re retardationvalue measured at 550 nm (Re550) in the range of 0 to 200 nm, an Rthretardation value measured at 550 nm (Rth550) in the range of 70 to 400nm, a thickness in the range of 10 to 70 μm, an Re retardation valuemeasured at 450 nm (Re450) in the range of 100 to 125 nm, and an Reretardation value measured at 590 nm (Re590) in the range of 120 to 160nm, said Re450 and Re590 values satisfying the condition ofRe590−Re450≧2 nm.

[0047] The invention still furthermore provides a liquid crystal displaycomprising a pair of polarizing plates and a liquid crystal cell of bendalignment mode provided between the plates, wherein at least onepolarizing plate is an elliptically polarizing plate which comprises afirst optically anisotropic layer comprising discotic molecules orientedin hybrid alignment, a second optically anisotropic layer comprising atleast one cellulose acetate film, and a polarizing membrane, saidpolarizing membrane being arranged as an outermost layer, said first andsecond optically anisotropic layers and said polarizing membrane beingso arranged that a direction giving the maximum refractive index inplane of the first optically anisotropic layer is oriented essentiallyat an angle of 45° to a transmission axis in plane of the polarizingmembrane and that a direction giving the maximum refractive index inplane of the second optically anisotropic layer is directed essentiallyparallel or perpendicular to a transmission axis in plane of thepolarizing membrane, wherein the cellulose acetate film of the secondoptically anisotropic layer contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,said cellulose acetate film having an Re retardation value measured at550 nm (Re550) in the range of 1 to 20 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 150 to 300 nm, and athickness in the range of 10 to 70 μm.

[0048] Moreover, the invention provides a liquid crystal displaycomprising a pair of polarizing plates and a liquid crystal cell of bendalignment mode provided between the plates, wherein at least onepolarizing plate is an elliptically polarizing plate which comprises afirst optically anisotropic layer comprising discotic molecules orientedin hybrid alignment, a second optically anisotropic layer comprising atleast one cellulose acetate film, and a polarizing membrane, saidpolarizing membrane being arranged as an outermost layer, said first andsecond optically anisotropic layers and said polarizing membrane beingso arranged that a direction giving the maximum refractive index inplane of the first optically anisotropic layer is oriented essentiallyat an angle of 450 to a transmission axis in plane of the polarizingmembrane and that a direction giving the maximum refractive index inplane of the second optically anisotropic layer is directed essentiallyparallel to a transmission axis in plane of the polarizing membrane,wherein the cellulose acetate film of the second optically anisotropiclayer contains 100 weight parts of cellulose acetate having an aceticacid content of 59.0 to 61.5% and 0.01 to 20 weight parts of an aromaticcompound having at least two aromatic rings, said cellulose acetate filmhaving an Re retardation value measured at 550 nm (Re550) in the rangeof 20 to 100 nm, an Rth retardation value measured at 550 nm (Rth550) inthe range of 150 to 300 nm, and a thickness in the range of 10 to 70 μm.

[0049] The thickness of the cellulose acetate film used in the opticalcompensatory sheet, the kind and the amount of the additive (thearomatic compound having at least two aromatic rings) and the productionconditions (e.g., condition in stretching the film) are adequatelycontrolled, and thereby the inventors have succeeded in opticallycompensating a liquid crystal cell without leaking light.

[0050] The inventors have also succeeded in providing an opticalcompensatory sheet (λ/4 plate) giving λ/4 in a wide wavelength regionwithout leaking light. For the purpose of that, the thickness ofcellulose acetate film, the kind and the amount of the additive (thearomatic compound having at least two aromatic rings) and the productionconditions (e.g., condition in stretching the film) are adequatelycontrolled. The provided λ/4 plate can remarkably improves the viewingangle of liquid crystal display.

[0051] Further, the invention provides an optical compensatory sheet(λ/4 plate) consisting of one cellulose acetate film and giving λ/4 in awide wavelength, and thereby makes it unnecessary to perform theconventional production step in which two polymer films are carefullylaminated so that the angle between them may be strictly controlled.

[0052] In the invention, in order to optically compensate a liquidcrystal cell, the cellulose acetate film used for the opticalcompensatory sheet is made to have an Re retardation value measured at550 nm (Re550) in the range of 0 to 200 nm and an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm.

[0053] Also in the invention, in order to prevent the transmittance fromincreasing (to prevent the leakage of light) at the peripheral area, thecellulose acetate film used for the optical compensatory sheet is madeto have a thickness in the range of 10 to 70 μm. A conventional thincellulose acetate film has such a low Rth value that it cannot fullyoptically compensate a liquid crystal cell. On contrast, however, thecellulose acetate film of the invention contains the additive by whichthe film can fully optically compensate a liquid crystal cell in spiteof being thin enough to prevent the leakage of light. Since thecellulose acetate film has a thickness in the range of 10 to 70 μm, theleakage of light is avoided without impairing treatablity in producingthe optical compensatory sheet or in laminating the compensatory sheetonto the polarizing membrane. Further, the optical compensatory sheet ofthe invention is thin enough to reduce both the production cost and thethickness of resultant liquid crystal display.

[0054] A polarizing plate comprises two protective films and apolarizing membrane provided between the films. The polarizing membraneis a stretched polyvinyl alcohol film adsorbed with iodine ordichromatic dye, and the protective film generally comprises a celluloseacetate film. If the aforementioned optical compensatory sheet is usedas one of the protective films, the optical compensatory function isgiven to the polarizing plate without increasing the element. Further,if a surface of the cellulose acetate film is saponified to have asurface energy of 55 to 75 mN/m, the adhesion to polyvinyl alcohol isenhanced to prepare a polarizing plate excellent in durability.Furthermore, when the surface of the cellulose acetate film issaponified, the saponifying conditions are adequately controlled so thatalkaline solution used for the saponification may be colored little andso that the saponification may not affect the optical characters of thecompensatory sheet.

[0055] If cellulose acetate having an acetic acid content less than59.0% is used, the aforementioned optical anisotropy can be easilyrealized. However, a film of such cellulose acetate has poor properties.In the invention, cellulose acetate having an acetic acid content of59.0 to 61.5% is used, and the above retardation values are achieved byother means (by adding the additive, and by controlling the productionconditions) to obtain a cellulose acetate film having both aimed opticalanisotropy and excellent properties.

[0056] The aforementioned optical compensatory sheet and a polarizingplate comprising that sheet as a protective film can be advantageouslyused in liquid crystal displays of VA (vertically aligned) mode, OCB(optically compensated bend) mode and TN (twisted nematic) mode, and adisplay of reflection type.

[0057] The optical compensatory sheet can be advantageously used in aliquid crystal display of bend alignment mode (OCB type).

[0058] The liquid crystal display of bend alignment mode is equippedwith an elliptically polarizing plate in which an optically compensatorysheet containing a discotic compound is used. For that opticallycompensatory sheet, a material giving high birefringence (e.g.,polycarbonate) has been conventionally used.

[0059] According to the invention, the polarizing plate used in thedisplay of bend alignment mode is composed of a polarizing membrane, anoptically anisotropic layer comprising a discotic compound (hereinafter“first optically anisotropic layer”) and at least one cellulose acetatefilm having particular optical characters (hereinafter “second opticallyanisotropic layer”).

[0060] The first optically anisotropic layer and the polarizing membraneare placed so that the average direction obtained by projecting normalof the disc plane of the discotic compound onto the cellulose acetatefilm may be essentially at the angle of 45° to the transmission axis inthe plane of polarizing membrane. Further, the second opticallyanisotropic layer and the polarizing membrane are placed so that theslow axis of the second anisotropic layer may be essentially parallel orperpendicular to the transmission axis in the plane of polarizingmembrane. The display of bend alignment mode having that structure givesa completely optically compensated image, and black spots are not seenat the corners of the displayed image even if the display is used for along time. Further, that display of OCB mode gives a display withoutleaking light.

[0061] In the present specification, the term “essentially parallel”means that the angle between the noticed directions is within the rangeof the strict angle ±5°. This angle allowance is preferably less than±4°, more preferably less than ±3°, most preferably less than ±20.

[0062] The terms “slow axis” and “transmission axis” mean the directionsgiving the maximum refractive index and the minimum refractive index,respectively.

BRIEF DESCRIPTION OF DRAWING

[0063]FIG. 1 schematically shows the basic structure of a liquid crystaldisplay of reflection type.

[0064]FIG. 2 is a sectional view illustrating a representativeembodiment of the guest-host liquid crystal display of reflection type.

[0065]FIG. 3 is a sectional view illustrating another representativeembodiment of the guest-host liquid crystal display of reflection type.

[0066]FIG. 4 is a sectional view schematically illustrating alignment ofliquid crystal molecules in a liquid crystal cell of bend alignmentmode.

[0067]FIG. 5 schematically shows an elliptically polarizing plateaccording to the invention.

[0068]FIG. 6 schematically shows a liquid crystal display of bendalignment mode according to the invention.

[0069]FIG. 7 schematically shows mechanism of optical compensation in aliquid crystal display of bend alignment mode.

[0070]FIG. 8 schematically shows various embodiments of the ellipticallypolarizing plate.

[0071]FIG. 9 schematically shows other embodiments of the ellipticallypolarizing plate.

DETAILED DESCRIPTION OF INVENTION

[0072] (Prevention of Light Leakage)

[0073] The inventors have studied, and found that the transmittance atthe peripheral part of the screen in the liquid crystal displayincreases to cause frame-like leakage of light by the following twomechanisms.

[0074] In the first mechanism, the cause is fluctuation of conditionssuch as heat and moisture under which the liquid crystal display works.

[0075] When used in a liquid crystal display, the optical compensatorysheet is normally fixed on a liquid crystal cell with an adhesive. Ifthe display is exposed to fluctuation of temperature and humidity, thecellulose acetate film used as the compensatory sheet expands orshrinks. Since the compensatory sheet is fixed, the expansion orshrinkage is repressed to cause internal stress in the film. The stressinduces birefringence in the film (photoelastic effect) to change theoptical character, and as a result the film leaks light.

[0076] In the second mechanism, the cause is thermal unevenness in theplane of the compensatory sheet. The thermal unevenness is given by, forexample, backlight in the liquid crystal display, and it inducesdistortion of the film. Consequently, the optical character is changedin the above manner to leak light.

[0077] Further, the inventors have found that a film of hydroxylgroup-containing polymer such as cellulose acetate is particularlyaffected by fluctuation of working conditions.

[0078] In order to prevent the sheet from leaking light, thecompensatory sheet is made to change the optical character little andfurther to keep thermal evenness.

[0079] The inventors have found that the change of optical characterrelates to the thickness, the photoelastic coefficient, the virtualdistortion caused by fluctuation of working conditions, and theelasticity of the compensatory sheet. Therefore, in order to remarkablyreduce the leakage of light, the compensatory sheet is made to be thin,to have a low photoelastic coefficient, to be distorted little byfluctuation of working conditions, and to have a small modulus ofelasticity. Further, if the compensatory sheet has a high thermalconductivity, heat in the sheet is evenly distributed to reduce theleakage of light.

[0080] According to the study of the inventors, it is particularlyeffective in preventing the leakage of light to make the celluloseacetate film thin enough. The transmittance relates to the product ofbirefringence and the thickness of the film (the product indicates phaseretardation). In fact, the transmittance increases with the increase ofthe phase retardation. Accordingly, if the cellulose acetate film ismade thin enough, small phase retardation is realized even ifbirefringence is generated in the same degree. Consequently, the thincellulose acetate film reduces the increase of transmittance at theperipheral part of the screen. However, if the film is too thin, othertroubles such as impairment of handling treatablity come up.

[0081] In consideration of balance between the prevention of lightleakage and the handling treatablity in producing the opticalcompensatory sheet, the thickness of the cellulose acetate film isdetermined as follows.

[0082] In the invention, the cellulose acetate film used as the opticalcompensatory sheet is made to have a thickness in the range of 10 to 70μm. The thickness is preferably in the range of 20 to 60 μm, morepreferably in the range of 30 to 50 μm.

[0083] The cellulose acetate film preferably has a thermal conductivityof 1 W/(m·K) or more.

[0084] In order to reduce the virtual distortion, it is preferred thatthe cellulose acetate film be biaxially stretched to promote planaralignment of the polymer molecules or that the film be made to have amoisture expansion coefficient of 30×10⁻⁵/% RH or less. The moistureexpansion coefficient is preferably 15×10⁻⁵-/% RH or less, morepreferably 10×10⁻⁵/% RH or less.

[0085] The cellulose acetate film preferably has a photoelasticcoefficient of 1.0×10⁻⁵ cm²/Kg or less.

[0086] The cellulose acetate film has a modulus of elasticity preferablyin the range of 3,000 MPa or less, more preferably in the range of 2,500Mpa or less.

[0087] (Retaradtion of Film)

[0088] The retardation values in plane (Re) and in the thicknessdirection (Rth) of the film are defined by the following formulas (I)and (II), respectively:

Re=(nx−ny)×d  (I)

Rth=[{(nx+ny)/2}−nz]×d.  (II)

[0089] In the formulas (I) and (II), nx is a refractive index along theslow axis (direction giving the maximum refractive index) in the planeof the film.

[0090] In the formulas (I) and (II), ny is a refractive index along thefast axis (direction giving the minimum refractive index) in the planeof the film.

[0091] In the formula (II), nz is a refractive index in the thicknessdirection of the film.

[0092] In the formulas (I) and (II), d is the thickness of the film interms of nm.

[0093] In the cellulose acetate film of the invention, the Reretardation value measured at 550 nm (Re550) is controlled in the rangeof 0 to 200 nm, and the Rth retardation value measured at 550 nm(Rth550) is controlled in the range of 70 to 400 nm.

[0094] If the optical compensatory sheet consists of the celluloseacetate film, the Re retardation value measured at 550 nm (Re550) iscontrolled preferably in the range of 20 to 70 nm.

[0095] If the optical compensatory sheet consists of the celluloseacetate film having an optically anisotropic layer provided thereon, theRe retardation value measured at 550 nm (Re550) is controlled preferablyin the range of 0 to 20 nm.

[0096] If one optical compensatory sheet is used in the liquid crystaldisplay, the Rth retardation value of the cellulose acetate filmmeasured at 550 nm (Rth550) is controlled preferably in the range of 150to 400 nm.

[0097] If two optical compensatory sheets are used in the liquid crystaldisplay, the Rth retardation value of the cellulose acetate filmmeasured at 550 nm (Rth550) is controlled preferably in the range of 70to 250 nm, more preferably in the range of 70 to 200 nm.

[0098] The cellulose acetate film has a birefringent index (Δn: nx−ny)measured at 550 nm preferably in the range of 0.00028 to 0.020, morepreferably in the range of 0.00196 to 0.01375, further preferably in therange of 0.00168 to 0.006875, most preferably in the range of 0.00275 to0.00458. The birefringent index in the thickness direction{(nx+ny)/2−nz} measured at 550 nm is preferably in the range of 0.001 to0.04.

[0099] (λ/4 Plate)

[0100] In the case where the optical compensatory sheet consisting ofthe cellulose acetate film is used as a λ/4 plate, the film iscontrolled to have an Re retardation value measured at 450 nm (Re450) inthe range of 100 to 125 nm and another Re retardation value measured at590 nm (Re590) in the range of 120 to 160 nm. These Re retardationvalues satisfy preferably the condition of Re590−Re450≧2 nm, morepreferably the condition of Re590−Re450≧5 nm, most preferably thecondition of Re590−Re450≧10 nm.

[0101] The Re retardation value measured at 450 nm (Re450) is preferablyin the range of 108 to 125 nm, the Re retardation value measured at 550nm (Re550) is preferably in the range of 125 to 142 nm, the Reretardation value measured at 590 nm (Re590) is preferably in the rangeof 130 to 152 nm, and the Re550 and Re590 values satisfy preferably thecondition of Re590−Re550≧2 nm, more preferably the condition ofRe590−Re550≧5 nm, most preferably the condition of Re590−Re550>10 nm.Further, Re550 and Re450 values preferably satisfy the condition ofRe550−Re450≧10 nm.

[0102] It is also preferred that the λ/4 plate (optical compensatorysheet) of the invention singly satisfy the condition of:

1≦(nx−nz)/(nx−ny)≦2

[0103] in which nx is a refractive index parallel to the slow axis inthe plane of the plate, ny is a refractive index perpendicular to theslow axis in the plane of the plate, and nz is a refractive index in thethickness direction.

[0104] The cellulose acetate film having the above optical characterscan be made of cellulose acetate containing the retardation-increasingagent described after.

[0105] The retardation values and its wavelength dependence of thecellulose acetate film can be controlled by (1) adjusting thecomposition (particularly, average acetic acid content) of celluloseacetate, (2) adjusting the kind and the amount of retardation increasingagent, and (3) adjusting the thickness of the film. In particular, bymeans of the above (2), a phase retarder can be made of celluloseacetate, which has been conventionally known as an optically isotropicmaterial.

[0106] The cellulose acetate film having the aforementioned opticalcharacters can be prepared from the following materials in the mannerdescribed below.

[0107] (Cellulose Acetate)

[0108] In the invention, cellulose acetate having an acetic acid contentof 59.0 to 61.5% is used. The acetic acid content is-preferably in therange of 59.5 to 61.3%.

[0109] The term “acetic acid content” means the amount of combinedacetic acid per one unit weight of cellulose. The acetic acid content isdetermined according to ASTM: D-817-91 (tests of cellulose acetate).

[0110] The cellulose ester has a viscosity average polymerization degree(DP) of preferably 250 or more, more preferably 290 or more.

[0111] Further, it is also preferred for the cellulose ester used in theinvention to have a narrow molecular weight distribution of Mw/Mn (Mwand Mn are weight and number average molecular weights, respectively)determined by gel permeation chromatography. The value of Mw/Mn ispreferably in the range of 1.0 to 1.7, more preferably in the range of1.3 to 1.65, most preferably in the range of 1.4 to 1.6.

[0112] In the cellulose acetate used in the invention, the substitutiondegree at 6-position is preferably high, in detail 0.88 or more. Thesubstitution degree at 6-position is preferably 32% or more, morepreferably 33% or more, most preferably 34% or more, based on the totalsubstitution degree at 2-, 3- and 6-positions.

[0113] If cellulose acetate is prepared by a normal method, the acetylsubstitution degree at 2- or 3-position is larger than that at6-position. Therefore, conditions for the synthesis must be particularlycontrolled to make the substitution degree at 6-position higher (0.88 ormore, 32% or more of the total substitution degree).

[0114] It is preferred to reduce the amount of sulfuric acid catalystused in the acetylation reaction and accordingly to continue thereaction for a long time. If the sulfuric acid catalyst is used in alarge amount, the reaction proceeds fast. In that case, however,sulfuric ester is formed with cellulose in a large amount according tothe amount of the catalyst. The formed ester is liberated to produceremaining hydroxyl groups after the reaction. Since the 6-position ishighly reactive, the sulfuric ester is much formed at the 6-position.Consequently, a large amount of sulfuric acid catalyst reduces theacetyl substitution degree at 6-position. Therefore, in order tosynthesize the cellulose acetate having a high substitution degree at6-position, the sulfuric acid catalyst must be used in as a small amountas possible, and the reaction time must be lengthened to make up forslowdown of the reaction rate.

[0115] The acetyl substitution degrees at 2-, 3- and 6-position can bemeasured by means of ¹³C-NMR after the cellulose acetate ispropionylated. The measurement of substitution degree is described indetail in Tezuka et al., Carbohydr. Res., 273(1995), 83-91.

[0116] The cellulose acetate having a high substitution degree at6-position is described in Japanese Patent Provisional No. 11(1999)-5851(Synthesis Examples 1 to 3).

[0117] (Retardation-Increasing Agent)

[0118] An aromatic compound having at least two aromatic rings is usedas a retardation-increasing agent for controlling the retardation of thecellulose acetate film.

[0119] The aromatic compound is added in an amount of 0.01 to 20 weightparts, preferably in an amount of 0.05 to 15 weight parts, morepreferably in an amount of 0.1 to 10 weight parts, based on 100 weightparts of cellulose acetate. Two or more aromatic compounds may be usedin combination.

[0120] In the present invention, “an aromatic ring” means not only anaromatic hydrocarbon ring but also an aromatic heterocyclic ring.

[0121] As the aromatic hydrocarbon ring, a six-membered ring (namely, abenzene ring) is particularly preferred.

[0122] The aromatic heterocyclic ring is generally unsaturated. Thearomatic heterocyclic ring is preferably a five-, six- or seven-memberedring, and more preferably a five- or six-membered ring. The aromaticheterocyclic ring generally has double bonds as many as possible. Theheteroatom in the ring preferably is nitrogen atom, sulfur atom oroxygen atom, and more preferably is nitrogen atom. Examples of thearomatic heterocyclic ring include furan ring, thiophene ring, pyrrolering, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring,imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring,pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring and1,3,5-triazine ring.

[0123] Preferred aromatic rings are benzene ring, furan ring, thiophenering, pyrrole ring, oxazole ring, thiazole ring, imidazole ring,triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and1,3,5-triazine ring. Benzene ring and 1,3,5-triazine ring are morepreferred The aromatic compound preferably contains at least one1,3,5-triazine ring.

[0124] The number of aromatic rings in the aromatic compound ispreferably in the range of 2 to 20, more preferably in the range of 2 to12, further preferably in the range of 2 to 8, and most preferably inthe range of 2 to 6.

[0125] The relation of the two or more aromatic rings is categorizedinto three cases, namely

[0126] (a) the case in which the aromatic rings form a condensed ring,

[0127] (b) the case in which the aromatic rings are connected through asingle bond, and

[0128] (c) the case in which the aromatic rings are connected through alinking group. In the case (c), a spirobond is not formed because therings are aromatic.

[0129] The relation of the aromatic rings may be any of the cases (a) to(c).

[0130] Examples of the condensed ring in the case (a) include indenering, naphthalene ring, azulene ring, fluorene ring, phenanthrene ring,anthracene ring, acenaphthylene ring, biphenylene ring, naphthacenering, pyrene ring, indole ring, isoindole ring, benzofuran ring,benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazolering, benzimidazole ring, benzotriazole ring, purine ring, indazolering, chromene ring, quinoline ring, isoquinoline ring, quinolizinering, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazinering, pteridine ring, carbazole ring, acridine ring, phenanthridinering, xanthene ring, phenazine ring, phenothiazine ring, phenoxthinering, phenoxazine ring and thianthrene ring. Preferred are naphthalenering, azulene ring, indole ring, benzoxazole ring, benzothiazole ring,benzimidazole ring, benztriazole ring and quinoline ring.

[0131] The single bond in the case (b) is preferably between carbonatoms of the two aromatic rings. Two or more single bonds may connectthe two aromatic rings to form an aliphatic ring or a non-aromatic ringbetween them.

[0132] The linking group in the case (c) is also preferably betweencarbon atoms of the two aromatic rings. The linking group is preferablyan alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—,—NH—, —S— and a combination thereof.

[0133] Examples of the linking group formed by the combination are shownbelow. In each of the following examples, the right and left terminalsmay be reversed.

[0134] c1: —CO—O—

[0135] c2: —CO—NH—

[0136] c3: -alkylene-O—

[0137] c4: —NH—CO—NH—

[0138] c5: —NH—CO—O—

[0139] c6: —O—CO—O—

[0140] c7: —O-alkylene-O—

[0141] c8: 13 CO-alkenylene-

[0142] c9: —CO-alkenylene-NH—

[0143] c10: —CO-alkenylene-O—

[0144] c11: -alkylene-CO—O-alkylene-O—CO-alkylene-

[0145] c12: —O-alkylene-CO—O-alkylene-O—CO-alkylene-O—

[0146] c13: —O—CO-alkylene-CO—O—

[0147] c14: —NH—CO-alkenylene-

[0148] c15: —O—Co-alkenylene-

[0149] The aromatic ring and the linking group may have substituentgroups.

[0150] Examples of the substituent group include halogen atoms (F, Cl,Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl,sulfamoyl, ureido, an alkyl group, an alkenyl group, an alkynyl group,an aliphatic acyl group, an aliphatic acyloxy group, an alkoxy group, analkoxycarbonyl group, an alkoxycarbonylamino group, an alkylthio group,an alkylsulfonyl group, an aliphatic amide group, an aliphaticsulfoneamide group, an aliphatic substituted amine group, an aliphaticsubstituted carbamoyl group, an aliphatic substituted sulfamoyl group,an aliphatic substituted ureido group and a non-aromatic heterocyclicgroup.

[0151] The alkyl group preferably has 1 to 8 carbon atoms. A chain alkylgroup is preferred to a cyclic one, and a straight chain alkyl group isparticularly preferred. The alkyl group may further have a substituentgroup (e.g., hydroxyl, carboxyl, an alkoxy group, an alkyl-substitutedamino group). Examples of the (substituted) alkyl group include methyl,ethyl, n-butyl, n-hexyl, 2-hydroxyethyl, 4-carboxybutyl, 2-methoxyethyland 2-diethylaminoethyl.

[0152] The alkenyl group preferably has 2 to 8 carbon atoms. A chainalkenyl group is preferred to a cyclic one, and a straight chain alkenylgroup is particularly preferred. The alkenyl group may further have asubstituent group. Examples of the alkenyl group include vinyl, allyland 1-hexenyl.

[0153] The alkynyl group preferably has 2 to 8 carbon atoms. A chainalkynyl group is preferred to a cyclic one, and a straight chain alkynylgroup is particularly preferred. The alkynyl group may further have asubstituent group. Examples of the alkynyl group include ethynyl,1-butynyl and 1-hexynyl.

[0154] The aliphatic acyl group preferably has 1 to 10 carbon atoms.Examples of the aliphatic acyl group include acetyl, propanoyl andbutanoyl.

[0155] The aliphatic acyloxy group preferably has 1 to 10 carbon atoms.Examples of the aliphatic acyloxy group include acetoxy.

[0156] The alkoxy group preferably has 1 to 8 carbon atoms. The alkoxygroup may further have a substituent group (e.g., another alkoxy group).Examples of the (substituted) alkoxy group include methoxy, ethoxy,butoxy and methoxyethoxy.

[0157] The alkoxycarbonyl group preferably has 2 to 10 carbon atoms.Examples of the alkoxycarbonyl group include methoxycarbonyl andethoxycarbonyl.

[0158] The alkoxycarbonylamino group preferably has 2 to 10 carbonatoms. Examples of the alkoxycarbonylamino group includemethoxycarbonylamino and ethoxycarbonylamino.

[0159] The alkylthio group preferably has 1 to 12 carbon atoms. Examplesof the alkylthio group include methylthio, ethylthio and octylthio.

[0160] The alkylsulfonyl group preferably has 1 to 8 carbon atoms.Examples of the alkylsulfonyl group include methanesulfonyl andethanesulfonyl.

[0161] The aliphatic amide group preferably has 1 to 10 carbon atoms.Examples of the aliphatic amide group include acetoamide The aliphaticsulfoneamide group preferably has 1 to 8 carbon atoms. Examples of thealiphatic sulfoneamide group include methanesulfoneamide,butanesulfoneamide and n-octanesulfoneamide.

[0162] The aliphatic substituted amine group preferably has 1 to 10carbon atoms. Examples of the aliphatic substituted amine group includedimethylamino, diethylamino and 2-carboxyethyl amino.

[0163] The aliphatic substituted carbamoyl group preferably has 2 to 10carbon atoms. Examples of the aliphatic substituted carbamoyl groupinclude methylcarbamoyl and diethylcarbamoyl.

[0164] The aliphatic substituted sulfamoyl group preferably has 1 to 8carbon atoms. Examples of the aliphatic substituted sulfamoyl groupinclude methylsulfamoyl and diethylsulfamoyl.

[0165] The aliphatic substituted ureido group preferably has 2 to 10carbon atoms. Examples of the aliphatic substituted ureido group includemethylureido.

[0166] Examples of the non-aromatic heterocyclic group includepiperidino and morpholino.

[0167] The retardation increasing agent has a molecular weight of 300 to800.

[0168] The retardation increasing agent has a boiling point of 260° C.or more. The boiling point can be measured by means of a commerciallyavailable apparatus (e.g., TG/DTA100, Seiko Electronics Co., Ltd.).

[0169] Concrete examples of the retardation-increasing agent aredescribed in Japanese Patent Provisional Publication Nos. 2000-111914,2000-275434 and PCT/JP 00/02619.

[0170] (Infrared Absorber)

[0171] An infrared absorber can be added to the cellulose acetate film,to adjust the retardation value at each wavelength.

[0172] The amount of the infrared absorber is preferably in the range of0.01 to 5 weight parts, more preferably in the range of 0.02 to 2 weightparts, further preferably in the range of 0.05 to 1 weight part, andmost preferably in the range of 0.1 to 0.5 weight parts, based on 100weight parts of cellulose ester. Two or more infrared absorbers may beused in combination.

[0173] The infrared absorber shows the maximum absorption preferably inthe wavelength region of 750 to 1,100 nm, more preferably in thewavelength region of 800 to 1,000 rm. It is also preferred for theinfrared absorber to have essentially no absorption in the visiblewavelength region.

[0174] As the infrared absorber, an infrared absorbing dye or pigment ispreferred. An infrared absorbing dye is particularly preferred.

[0175] The infrared absorbing dyes include organic compounds andinorganic ones. Organic infrared absorbing dyes are preferred. Examplesof the organic infrared absorbing dyes include cyanine compounds, metalchelate compounds, aminium compounds, diimmonium compounds, quinonecompounds, squarilium compounds and methine compounds. The infraredabsorbing dyes are described in “Shikizai (color material) [written inJapanese]”, 61(4), pp. 215-226 (1988) and “Kagaku to Kogyo (chemistryand industry [written in Japanese]”, 43-53 (1986, May).

[0176] In view of infrared absorbance and absorption spectrum, infraredabsorbing dyes developed in the field of silver halide photographicphotosensitive material are preferred. Examples of the infraredabsorbing dyes developed in the field of silver halide photographicphotosensitive material include dihydroperimidine squarilium dye(described in U.S. Pat. No. 5,380,635 and Japanese Patent ApplicationNo. 8(1996)-189817), cyanine dye (described in Japanese PatentProvisional Publication Nos. 62(1987)-123454, 3(1991)-138640,3(1991)-211542, 3(1991)-226736, 5(1993)-313305 and 6(1994)-43583,Japanese Patent Application No. 7(1995)-269097 and European Patent No.0,430,244), pyrylium dye (described in Japanese Patent ProvisionalPublication Nos. 3(1991)-138640 and 3(1991)-211542), diimmonium dye(described in Japanese Patent Provisional Publication Nos.3(1991)-138640 and 3(1991)-211542), pyrazolopyridone dye (described inJapanese Patent Provisional Publication No. 2(1990)-282244), indoanilinedye (described in Japanese Patent Provisional Publication Nos.5(1993)-323500 and 5(1993)-323501), polymethine dye (described inJapanese Patent Provisional Publication Nos. 3(1991)-26765 and4(1992)-190343, and European Patent No. 0,377,961), oxonol dye(described in Japanese Patent Provisional Publication No. 3(1991)-9346),anthraquinone dye (described in Japanese Patent Provisional PublicationNo. 4(1992)-13654), naphthalocyanine dye (described in U.S. Pat. No.5,009,989), and naphtholactum dye (described in European Patent No.0,568,267).

[0177] (Production of Cellulose Acetate Film)

[0178] The cellulose acetate film is preferably prepared according to asolvent cast method. As the solvent, an organic solvent is preferablyused. The solvent cast method comprises the steps of dissolvingcellulose ester in an organic solvent to prepare a solution (dope) andcasting the dope to prepare a film.

[0179] The organic solvent is preferably selected from the groupconsisting of an ether having 3 to 12 carbon atoms, a ketone having 3 to12 carbon atoms, an ester having 3 to 12 carbon atoms and a halogenatedhydrocarbon having 1 to 6 carbon atoms.

[0180] The ether, ketone and ester may have a cyclic structure. Acompound having two or more functional groups of ether (—O—), ketone(—CO—) and ester (—COO—) can be also used as the organic solvent. Theorganic solvent can have another functional group such as alcoholichydroxyl. In the case where the organic solvent has two or more of theabove functional groups, the number of the carbon atoms is defined as acompound having one optionally selected from those groups.

[0181] Examples of the ether having 3 to 12 carbon atoms includediisopropyl ether, dimethoxymethane, 1,4-dioxane, 1,3-dioxolane,tetrahydrofuran, anisole and phenetol.

[0182] Examples of the ketone having 3 to 12 carbon atom includeacetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone,cyclohexanone and methylcyclohexanone.

[0183] Examples of the ester having 3 to 12 carbon atoms include ethylformate, propyl formate, pentyl formate, methyl acetate, ethyl acetate,and pentyl acetate.

[0184] Examples of the compounds having two or more kinds of functionalgroups include 2-ethoxyethyl acetate, 2-methoxyethanol and2-butoxyethanol.

[0185] The halogenated hydrocarbon has preferably one or two carbonatoms, more preferably one carbon atom. The halogen atom of thehalogenated hydrocarbon is preferably chlorine. The ratio of hydrogensubstituted with halogen is preferably in the range of 25 to 75 mol. %,more preferably in the range of 30 to 70 mol. %, further preferably inthe range of 35 to 65 mol. %, and most preferably in the range of 40 to60 mol. %. Methylene chloride is a representative halogenatedhydrocarbon.

[0186] Two or more organic solvents can be used in combination.

[0187] A cellulose acetate solution can be prepared according to aconventional method. The conventional method means that the solution isprepared at a temperature of not lower than 0° C. (room temperature orelevated temperature). The preparation of the solution can be conductedby means of a process and apparatus used in a conventional solvent castmethod. The conventional method preferably uses a halogenatedhydrocarbon (particularly methylene chloride) as an organic solvent.

[0188] The amount of cellulose acetate is so adjusted that a preparedsolution contains cellulose acetate in an amount of 10 to 40 wt. %. Theamount of cellulose acetate is more preferably 10 to 30 wt. %. Anoptional additive (described below) can be added to an organic (main)solvent.

[0189] The solution can be prepared by stirring cellulose acetate and anorganic solvent at an ordinary temperature (0 to 40° C.). A solution ofhigh concentration may be prepared by stirring them at an elevatedtemperature under a high pressure. In that case, cellulose acetate andthe organic solvent are placed in a closed vessel, and are stirred at anelevated temperature under a high pressure. The temperature is set to behigher than the boiling point at atmospheric pressure but lower than theboiling point of the solvent at the high pressure. Accordingly, theheating temperature is normally not lower than 40° C., preferably in therange of 60 to 200° C., and more preferably in the range of 80 to 110°C.

[0190] The components can be preliminary dispersed coarsely, and thecoarse dispersion can be placed in the vessel. Otherwise, the componentscan be also introduced into the vessel in series. The vessel should beequipped with a stirring device. A pressure in the vessel can be formedby introducing an inert gas such as nitrogen gas into the vessel, or byheating and evaporating the solvent to increase the vapor pressure.Otherwise, the components can be added to the vessel at a high pressureafter the vessel is sealed.

[0191] The vessel is preferably heated from the outside. For example,the vessel can be heated with a jacket type heating apparatus.Otherwise, liquid heated with a plate heater placed outside of thevessel may be circulated through a pipe wound around the vessel, to heatthe whole vessel.

[0192] The mixture is preferably stirred with a propeller mixer providedin the vessel. The wing of the propeller preferably has a lengthreaching the inside wall of the vessel. Further, at the tip of the wing,a scratching mean is provided to scratch and renew the mixture attachedon the inside wall.

[0193] In the vessel, various meters such as pressure gauge andthermometer may be provided. The components are dissolved in the solventin the vessel. The thus-prepared dope may be cooled and then taken outof the vessel, or may be taken out and then cooled with a heatexchanger.

[0194] The solution can be also prepared according to a coolingdissolution method. According to the cooling dissolution method,cellulose acetate can be dissolved even in organic solvents in whichcellulose acetate cannot be dissolved according to a conventionalmethod. Further, according to the method, cellulose acetate can berapidly and homogeneously dissolved in an organic solvent in whichcellulose acetate can be dissolved by a conventional process.

[0195] First in the process of cooling dissolution method, the polymeris gradually added with stirring into an organic solvent at roomtemperature.

[0196] The amount of the polymer in the mixture is preferably in therange of 10 to 40 wt. %, more preferably in the range of 10 to 30 wt. %.Various additives described below may be added in the mixture.

[0197] At the next stage, the prepared mixture is cooled to atemperature of −100 to −10° C., preferably −80 to −10° C., morepreferably −50 to −20° C., most preferably −50 to −30° C. The coolingprocedure can be carried out, for example, with dry ice-methanol bath(−75° C.) or with cooled ethylene glycol solution (−30 to −20° C.).Through the cooling procedure, the mixture is solidified.

[0198] The cooling rate is preferably 4° C./minute or more, morepreferably 8° C./minute or more, and most preferably 12° C./minute ormore. The cooling rate is preferably as fast as possible. However, atheoretical upper limit of the cooling rate is 10,000° C. per second, atechnical upper limit is 1,000° C. per second, and a practical upperlimit is 100° C. per second. The cooling rate means the change oftemperature at the cooling step per the time taken to complete thecooling step. The change of temperature means the difference between thetemperature at which the cooling step is started and the temperature atwhich the cooling step is completed.

[0199] The cooled mixture is then warmed to a temperature of 0 to 200°C., preferably 0 to 150° C., more preferably 0 to 120° C., mostpreferably 0 to 50° C. Through the warming procedure, the polymer isdissolved in the organic solvent. For warming, the mixture may be leftat room temperature or may be heated in a warm bath.

[0200] The warming rate is 4° C./minute or more, more preferably 8°C./minute or more, and most preferably 12° C./minute or more. Thewarming rate is preferably as fast as possible. However, a theoreticalupper limit of the cooling rate is 10,000° C. per second, a technicalupper limit is 1,000° C. per second, and a practical upper limit is 100°C. per second. The warming rate means the change of temperature at thewarming step per the time taken to complete the warming step. The changeof temperature means the difference between the temperature at which thewarming step is started and the temperature at which the warming step iscompleted.

[0201] Thus, a homogeneous solution can be prepared. If the polymer isnot sufficiently dissolved, the cooling and warming procedures may berepeated. It can be judged by observation with the eyes whether thepolymer is sufficiently dissolved or not.

[0202] In the process of cooling dissolution method, a sealed vessel ispreferably used to prevent contamination of water, which may be causedby dew condensation at the cooling step. Further, the mixture may becooled under a reduced pressure so that the time taken to complete thecooling step can be shortened, and hence a vessel resisting pressure ispreferably used to conduct the procedures under a reduced pressure.

[0203] According to differential scanning calorimetric measurement(DSC), a 20 wt. % solution prepared by dissolving cellulose acetate(acetic acid content: 60.9%, viscosity average polymerization degree:299) in methyl acetate through the cooling dissolution process has apseudo-phase transition point between gel and sol at about 33° C. Belowthat temperature, the solution is in the form of homogeneous gel. Thesolution, therefore, must be kept at a temperature above thepseudo-phase transition point, preferably at a temperature higher thanthe pseudo-phase transition point by about 10° C. The pseudo-phasetransition point depends upon various conditions such as the organicsolvent, the acetic acid content, the viscosity average polymerizationdegree and the concentration of cellulose acetate.

[0204] The polymer film is formed from the prepared polymer solution(dope) according to the solvent cast method.

[0205] The dope is cast on a drum or a band, and the solvent isevaporated to form a film. The solid content of the dope is preferablycontrolled in the range of 18 to 35%. The surface of the drum or band ispreferably beforehand polished to be a mirror. The casting and dryingsteps of the solvent cast method are described in U.S. Pat. Nos.2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704,2,739,069, 2,739,070, British Patent Nos. 640,731, 736,892, JapanesePatent Publication Nos. 45(1970)-4554, 49(1974)-5614, Japanese PatentProvisional Publication Nos. 60(1985)-176834, 60(1985)-203430 and62(1987)-115035.

[0206] The surface temperature of the drum or band is preferably 10° C.or below. After cast on the drum or band, the dope is blown with air for2 seconds or more to dry. The formed film is then peeled, and blown withhot air whose temperature is successively changed from 100° C. to 160°C. in order to evaporate remaining solvent. This procedure is describedin Japanese Patent Publication No. 5(1993)-17844. The procedure canshorten the time taken to complete the steps of cooling to peeling. Forperforming the procedure, the cast dope must gel at the surfacetemperature of the drum or band.

[0207] From the prepared dope, two or more layers can be formedaccording to the simultaneous casting (co-casting) method. Also in thatcase, the cellulose acetate film is preferably produced according to thesolvent cast method. The dope is cast on a drum or a band, and thesolvent is evaporated to form a film. The solid content of the dope ispreferably controlled in the range of 10 to 40%. The surface of the drumor band is preferably beforehand polished to be a mirror.

[0208] In the case where two or more cellulose acetate solutions areused, the solutions may be cast from nozzles provided at intervals inthe transferring direction of the support to form a layered film. Thismethod is described in, for example, Japanese Patent ProvisionalPublication Nos. 61(1986)-158414, 1(1989)-122419 and 11(1999)-198285.The solutions may be simultaneously cast from two nozzles to form alayered film. This method is described in, for example, Japanese PatentPublication No. 60(1985)-27562, Japanese Patent Provisional PublicationNos. 61(1986)-94724, 61(1986)-947245, 61(1986)-104813, 61(1986)-158413and 6(1994)-134933.

[0209] Further, the method described in Japanese Patent ProvisionalPublication No. 56(1981)-162617 can be also adopted. In that method, ahighly viscous cellulose acetate solution is enclosed with a low viscousone, and then the thus-combined solutions are simultaneously extrudedand cast.

[0210] Furthermore, the method described in, for example, JapanesePatent Publication No. 44(1969)-20235 may be adopted. In the method, afilm is beforehand formed from a solution extruded out of one of twonozzles. After the formed film is peeled and reversely placed on thesupport, another solution is extruded from the other nozzle to cast ontothe film (on the surface having faced to the support) to form a layeredfilm.

[0211] The cellulose acetate solutions may be the same or different fromeach other. If some functional layers are to be formed, each celluloseacetate solution corresponding to each function may be extruded fromeach nozzle. Further, the cellulose acetate solution of the inventionmay be cast simultaneously with other dopes for other functional layers(e.g., adhesive layer, dye layer, antistatic layer, antihalation layer,ultraviolet layer, polarizing layer.

[0212] In the case where a thick film having a single layer is formed bythe conventional solvent cast method, it is necessary to extrude a dopeof high concentration and high viscosity. That dope is generally sounstable that solid particles are often deposited, and that the formedfilm often has poor evenness. If the viscous dope is extrudedsimultaneously from plural nozzles onto the support, a thick film havingexcellent evenness can be prepared. Further, since the thick dope israpidly dried, the film can be rapidly produced.

[0213] A plasticizer can be added to the cellulose acetate film toimprove the mechanical strength. The plasticizer has another function ofshortening the time for the drying process. Phosphoric esters andcarboxylic esters are normally used as the plasticizer. Examples of thephosphoric esters include triphenyl phosphate (TPP) and tricresylphosphate (TCP). Examples of the carboxylic esters include phthalicesters and citric esters. Examples of the phthalic esters includedimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate(DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) anddiethylhexyl phthalate (DEHP). Examples of the citric esters includetriethyl o-acetylcitrate (OACTE) and tributyl o-acetylcitrate (OACTB).Examples of the other carboxylic esters include butyl oleate,methylacetyl ricinoleate, dibutyl sebacate and various trimelliticesters. Phthalic ester plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) arepreferred. Further, DEP and DPP are particularly preferred.

[0214] The amount of the plasticizer is preferably in the range of 0.1to 25 wt. %, more preferably in the range of 1 to 20 wt. %, and mostpreferably in the range of 3 to 15 wt. % based on the amount ofcellulose acetate.

[0215] Deterioration inhibitors (e.g., anti-oxidizing agent, peroxidedecomposer, radical inhibitor, metal inactivating agent, oxygenscavenger, amine) can be incorporated into the cellulose acetate film.The deterioration inhibitors are described in Japanese PatentProvisional Publication Nos. 3(1991)-199201, 5(1993)-1907073,5(1993)-194789, 5(1993)-271471 and 6(1994)-107854. The deteriorationinhibitor is preferably added in the range of 0.01 to 1 wt. %, and morepreferably in the range of 0.01 to 0.2 wt. % based on the amount of theprepared solution (dope). If the amount is less than 0.01 wt. %, theeffect of the deterioration inhibitor cannot be expected. If the amountis more than 1 wt. %, the inhibitor would bleed out on the surface ofthe film. Butyrated hydroxytoluene (BHT) and tribenzylamine (TBA) areparticularly preferred deterioration inhibitors.

[0216] (Polyesterurethane)

[0217] The cellulose acetate film preferably contains polyesterurethaneto improve the mechanical characters. The polyesterurethane ispreferably prepared from isocyanate and the polyester represented by thefollowing formula (1), and is further preferably soluble indichloromethane.

H—(—O—(CH₂)_(q)—OOC—(CH₂)_(m)—CO)_(n)—(CH₂)_(q)—OH  (1)

[0218] In the formula, q is an integer of 2 to 4, m is an integer of 2to 4, and n is an integer of 1 to 100.

[0219] The structuring polyester consists of a glycol part and a dibasicacid part. The glycol part is derived from ethylene glycol,1,3-propanediol or 1,4-butanediol. The dibasic acid part is derived fromsuccinic acid, glutamic acid or adipic acid. The polyester has hydroxylsat both terminals. The polymerization degree n is in the range of 1 to100, and the preferred degree depends upon the used glycol and dibasicacid. The polyester preferably has a molecular weight in the range of1,000 to 4,500.

[0220] The polyesterurethane resin soluble in dichloromethane isprepared by the reaction between isocyanate and the polyesterrepresented by the above formula (1), and generally has a repeating unitrepresented by the following formula (2).

CONH—R—NHCO—(—O—(CH₂)_(q)—OOC—(CH₂)_(m)—CO)_(n)—O—(CH₂)_(q)—O—)—  (2)

[0221] In the formula, q is an integer of 2 to 4, m is an integer of 2to 4, n is an integer of 1 to 100, and R is a divalent atomic groupresidue.

[0222] Examples of the divalent atomic group residue are shown below.

[0223] Examples of the isocyanate used for preparing thepolyesterurethane resin include polymethylenediisocyanate (generalformula: OCN(CH₂)_(p)NCO in which p is an integer of 2 to 8) such asethylene diisocyanate, trimethylene diisocyanate, tetramethylenediisocyanate and hexamethylene diisocyanate; aromatic diisocyanate suchas p-phenylene diisocyanate, tolylene diisocyanate, p,p′-diphenylmethanediisocyanate and 1,5-naphthylene diisocyanate; and m-xylenediisocyanate. Those examples by no means restrict the invention.Tolylene diisocyanate, m-xylene diisocyanate and tetramethylenediisocyanate are preferred because they are easily obtained and stableenough to treat. Further, they have excellent compatibility withcellulose acetate when they turn into polyurethane.

[0224] The molecular weight of the polyesterurethane resin is preferablyin the range of 2,000 to 50,000, and is optionally selected according tothe kind and the molecular weight of the structuring polyesters andlinking diisocyanates. The molecular weight is further preferably in therange of 5,000 to 15,000 because the polyesterurethane resin having thatmolecular weight improves mechanical characters of the resultant filmand has good compatibility with cellulose acetate.

[0225] The polyesterurethane resin soluble in dichloromethane can beeasily prepared through the steps of mixing isocyanate and thepolyesterdiols of the formula (1), and heating and stirring the mixture.

[0226] The polyesters represented by the formula (1) can be easilyprepared through the thermal fusion condensation with polyesterifying orester-exchanging reaction between corresponding bibasic acids (or alkylesters thereof) and glycols, or through the interfacial condensationbetween acid chlorides thereof and glycols. In the reactions, theconditions are controlled so that the resultant polyester has hydroxylsat the terminal position.

[0227] The dichloromethane-soluble polyesterurethane resin used in theinvention has excellent compatibility with cellulose acetate having anacetic acid content of 58% or more. In fact, 200 weight parts of thepolyesterurethane having a molecular weight of 10,000 or less ismiscible even with 100 weight parts of acetyl cellulose, although itscompatibility slightly depends upon the resin structure.

[0228] Accordingly, in the case where the polyesterurethane resin isincorporated in the cellulose acetate to improve the mechanicalcharacters of the resultant film, the content of polyesterurethane isproperly determined according to the kind and molecular weight of theurethane resin and to the aimed mechanical characters.

[0229] If the mechanical characters are to be improved with theproperties of cellulose acetate maintained, the content of thepolyesterurethane resin is preferably in the range of 0.1 to 30 weightparts based on 100 weight parts of cellulose acetate.

[0230] The polyesterurethane resin is stable enough not to be decomposedat 180° C. or below. Since this dichloromethane-solublepolyesterurethane resin has excellent compatibility with celluloseacetate having an acetic acid content of 58% or more, a highlytransparent film can be formed from the mixture thereof. Further, havinga high average molecular weight, the polyesterurethane evaporates littleeven at high temperature while a conventional low molecular-weightplasticizer easily vaporizes. Accordingly, a film prepared from themixture of the polyesterurethane and the cellulose acetate causes lesstrouble (such as evaporation and migration of plasticizer) than knownfilms containing conventional plasticizers.

[0231] The polyesterurethane enhances the bending and tearing strengthsof the cellulose acetate film at high and low temperatures, andaccordingly the film is hardly broken. Hitherto, for enhancing themechanical strengths, low molecular-weight plasticizer has beenconventionally used. However, although the conventional method improvesthe film durability to a certain degree under the conditions of roomtemperature and high humidity, it cannot fully prevent the film fromlosing flexibility under the conditions of low temperature and highhumidity. Even if much amount of low molecular-weight plasticizer isused for the purpose of improving the mechanical characters, themechanical characters are actually remarkably impaired.

[0232] The cellulose acetate containing the dichloromethane-solublepolyesterurethane resin has tensile strength impaired a little accordingto the content of the resin. However, the degree of impairment isrelatively small as compared with the case where low molecular-weightplasticizer is used. On the other hand, with respect to bendingstrength, a film made of the cellulose acetate containing thepolyesterurethane resin is as strong as one without plasticizer.Further, the polyesterurethane resin prevents the plasticizer frommigration at low and high temperatures, and hence gives a flexible,transparent and glossy cellulose acetate film that hardly adheres toother films.

[0233] (Highly thermo-conductive particles)

[0234] The cellulose acetate film preferably has a thermal conductivityof 1 W/(m·K) or more. The thermal conductivity is preferably as high aspossible, but is generally 10 W/(m·K) or less if the film is prepared inthe following manner.

[0235] For controlling the thermal conductivity of cellulose acetatefilm, highly thermo-conductive particles are preferably added into thedope for preparing the film. Further, on a surface of the celluloseacetate film, a thermo-conductive layer containing highlythermo-conductive particles may be provided to control the thermalconductivity. A polymer containing highly thermo-conductive particlesmay be co-cast with cellulose acetate, or may be applied on thecellulose acetate film to form the thermo-conductive layer.

[0236] Examples of the highly thermo-conductive particles includeparticles of aluminum nitride, silicon nitride, boron nitride, magnesiumnitride, silicon carbide, aluminum oxide, zinc oxide, magnesium oxide,carbon, diamond and metals. The particles are preferably transparent notto deteriorate transparency of the film.

[0237] The amount of thermo-conductive particles is preferably in therange of 5 to 100 weight parts based on 100 weight parts of celluloseacetate. If it is less than 5 weigh parts, the thermal conductivity isinsufficiently improved. On the other hand, if the amount is more than100 weight parts, it is difficult to form the film and the resultantfilm is fragile.

[0238] The highly thermo-conductive particles have an average particlesize of preferably 0.05 to 80 μm, more preferably 0.01 to 10 μm. Theparticles may be spherical or needle-like.

[0239] In the invention, the thermal conductivity of cellulose acetatefilm is measured in the following manner.

[0240] First, a sample film is placed between a copper heater case and acopper plate in TO-3 type hater, and is pressed by 10%. The film is thenkept for 4 minutes while the copper heater case is electrified at 5 W,and the temperature difference between the case and the plate ismeasured. From the obtained date, the thermal conductivity is calculatedaccording to the formula:

[0241] thermal conductivity {W/(m·K)}={electric power (W)×thickness(m)}/{temperature difference (K) x measured area (m²)}.

[0242] (Stretching of Cellulose Acetate Film)

[0243] The cellulose acetate film is preferably stretched to control theretardation and to reduce the virtual distortion. Since the virtualdistortion is reduced in the stretching direction, it is preferred tostretch the film biaxially to reduce the distortion in all directions inthe film plane.

[0244] The stretching ratio is preferably in the range of 3 to 100%.

[0245] The biaxial stretching may be carried out simultaneously orsuccessively. In consideration of continuous production, the film ispreferably subjected to successive biaxial stretching. The film formedfrom the cast dope is peeled from the drum or band, and is firstlaterally and then longitudinally stretched. It may be firstlongitudinally and then laterally stretched.

[0246] The lateral stretching is carried out in the manner described in,for example, Japanese Patent Provisional Publication Nos.62(1987)-115035, 4(1992)-152125, 4(1992)-284211, 4(1992)-298310 and11(1999)-48271. The film is stretched at room temperature or elevatedtemperature. The temperature is preferably not higher than glasstransition temperature of the film. The film can be stretched under drycondition, and this fact is advantageous particularly in the case wherethe solvent remains in the film. For stretching the film longitudinally,rollers conveying the film are, for example, controlled so that thespeed of peeling the film may be slower than that of winding the film.On the other hand, for stretching the film laterally, the film may beconveyed while tensed laterally with a tenter to widen gradually.Further, it is also possible to stretch the film with a stretchingmachine (preferably, uniaxially with a long stretching machine). Thestretching ratio (ratio of gained length per original length) ispreferably in the range of 5 to 50%, more preferably in the range of 10to 40%, most preferably in the range of 15 to 35%.

[0247] The steps of casting to post-drying may be carried out under airatmosphere or inert gas (e.g., nitrogen gas) atmosphere. The celluloseacetate film of the invention can be wound up by means of a generallyused winding machine according to the constant tension method, theconstant torque method, the taper tension method or the programmedtension control method with constant internal stress.

[0248] (Moisture Expansion Coefficient)

[0249] When humidity is changed with the temperature not changed, thefilm generally expands. A moisture expansion coefficient indicates thegained length of the expanded film.

[0250] In order to prevent the transmittance at the peripheral part ofthe screen from increasing, the moisture expansion coefficient ispreferably 30×10⁻⁵/% RH or less, more preferably 15×10⁻⁵/% RH or less,most preferably 10×10⁻⁵/% RH or less. The moisture expansion coefficientis preferably as small as possible, but is normally 1.0×10⁻⁵ /% RH ormore.

[0251] The moisture expansion coefficient is measured in the followingmanner.

[0252] The prepared polymer film (phase retarder) is cut into ten pieces(5 mm×20 mm). One end of each piece was fixed, and a weight of 0.5 g issuspended from the other end. The hanging piece is left under theconditions of the temperature of 25° C. and the relative humidity of 20%RH (R₀) for 10 minutes, and then the length (L₀) is measured. Thehumidity is then changed to 80% RH (R₁) while the temperature is kept25° C., and the length (L₁) is measured. From the obtained date, themoisture expansion coefficient is calculated according to the followingformula. With respect to the ten pieces, the measurement is repeated andthe obtained values are averaged.

Moisture expansion coefficient [/% RH]={(L ₁ −L ₀)/L ₀}/(R ₁ −R ₀)

[0253] The less free volume a polymer film has, the less its dimensionchanges. The free volume greatly depends upon the amount of remainingsolvent used in forming the film. The less the solvent remains, the lessthe dimension changes.

[0254] For reducing the remaining solvent, the film is generally driedat a high temperature for a long time. However, if the drying time istoo long, the productivity is naturally impaired. Accordingly, theamount of the remaining solvent is preferably in the range of 0.01 to 1wt. %, more preferably in the range of 0.02 to 0.07 wt. %, mostpreferably in the range of 0.03 to 0.05 wt. %.

[0255] If the amount of remaining solvent is properly controlled, apolarizing plate having optical compensatory function can be produced atsmall cost with high productivity.

[0256] Further, a compound having hydrophobic groups is preferablyincorporated to reduce the dimensional change. The compound havinghydrophobic groups is not particularly restricted as long as it containshydrophobic groups such as alkyl group and phenyl group, but ispreferably selected from the materials described above as theplasticizer and the deterioration inhibitor added into celluloseacetate. Preferred examples of the compound include triphenyl phosphate(TPP) and tribenzylamine (TBA).

[0257] The amount of the compound having hydrophobic groups ispreferably in the range of 0.01 to 10 wt. %, more preferably in therange of 0.1 to 5 wt. %, most preferably in the range of 1 to 3 wt. %,base on the amount of the prepared solution (dope).

[0258] The amount of remaining solvent is measured in the followingmanner. First, a certain amount of the sample is dissolved inchloroform. The prepared solution is then measured through a gaschromatography (GC18A, Shimadzu Seisakusho Ltd.).

[0259] In the solvent cast method, a film is formed from a solution(dope) containing polymer material dissolved in solvent. The film isthen dried while it is on the drum (or band) and while it is conveyed,as described below. The film on the drum (or band) is preferably driedslowly at a temperature below the boiling point of the solvent (if it isabove the boiling point, bubbles are formed). The film being conveyed isdried at a temperature preferably in the range of the glass transitionpoint ±30° C., more preferably in the range of the glass transitionpoint ±20° C.

[0260] (Surface Treatment of Cellulose Acetate Film)

[0261] The cellulose acetate film is preferably subjected to surfacetreatment. Examples of the surface treatment include saponificationtreatment, plasma treatment, flame treatment and ultraviolet (UV)treatment. The saponification treatment includes acid saponificationtreatment and alkali saponification treatment. The plasma treatmentincludes glow discharge treatment and corona discharge treatment.Further, an undercoating layer is preferably provided as described inJapanese Patent Provisional Publication No. 7(1995)-333433.

[0262] The film after the surface treatment has a surface energy ofpreferably 55 mN/m or more, more preferably in the range of 60 to 75mN/m. If such cellulose acetate film is used as the transparentprotective film of the polarizing plate, the adhesion between the filmand the polarizing membrane is improved. In the case where an opticallyanisotropic layer is formed on the cellulose acetate film, it has beenhitherto necessary to provide a gelatin undercoating layer for ensuringthe adhesion between the cellulose acetate film and the orientationlayer. However, if the cellulose acetate film having a surface energy of55 to 75 mN/m is used, the gelatin undercoating layer can be omitted. Inorder to keep the planeness of the film, the film is preferably kept ata temperature below the glass transition point (Tg), namely at atemperature of not more than 150° C.

[0263] In the case where the optical compensatory sheet is used as thetransparent protective film of the polarizing plate, the celluloseacetate film is preferably subjected to acid or alkali saponificationtreatment for improving adhesion to the polarizing membrane.

[0264] The surface energy can be measured by the contact angle method,the wet heating method or the adsorption method, which are described in“The basic theory and application of wetting (written in Japanese)”,published by Realize Co., Ltd, 1989. The contact angle method ispreferred. In that method, two solutions having known surface energiesare dropped onto the cellulose acetate film. The contact angle of eachdrop is measured, and the surface energy of the film is calculated fromthe measured contact angles. The contact angle is, by definition, anangle (including the drop) between the film surface and the tangent ofthe drop surface at the crossing point. The alkaline saponificationtreatment preferably comprises the steps of immersing the celluloseacetate film in an alkaline solution, neutralizing the film with anacidic solution, washing with water and drying. Examples of the alkalinesolution include aqueous solutions of potassium hydroxide and sodiumhydroxide. The normality of hydroxyl ion in the alkali solution ispreferably in the range of 0.1 to 3.0 N, more preferably in the range of0.5 to 2.0 N. The alkaline solution is kept at a temperature preferablyin the range of room temperature to 90° C., more preferably in the rangeof 40 to 70° C.

[0265] The alkali is preferably an alkali metal hydroxide such aspotassium hydroxide and sodium hydroxide. The alkaline solutionpreferably has a pH value of 10 or more. It is preferred to immerse onlythe film surface facing to the polarizing membrane, but both surfaces ofthe cellulose acetate film may be immersed. The time for immersing ispreferably in the range of 1 to 300 seconds, more preferably in therange of 5 to 240 seconds. The temperature for the saponificationreaction is preferably in the range of 25 to 70° C., more preferably inthe range of 35 to 60° C. After immersed in the alkaline solution, thefilm is preferably washed with water.

[0266] In the case where only one surface is subjected to the alkalinesaponification treatment, it is preferably washed with water after thealkaline solution is applied. In this case, the solvent of the alkalinesolution preferably does not swell the cellulose acetate film, and henceis preferably an alcohol (e.g., isopropanol, butanol). Further, amixture containing other solvents (such as propylene glycol and water)for improving coating characters and alkali solubility may be used asthe solvent.

[0267] The Re550 of the thus treated cellulose acetate film is changedthrough the above saponification by 3 nm or less. Further, the abovesaponification does not yellow the alkaline solution.

[0268] The corona discharge treatment comprises the steps of applyinghigh voltage between a roll of dielectrics and an electrode connectingto a high voltage generator, and placing or moving the cellulose acetatefilm in corona discharge generated between the roll and the electrode.In the present specification, the frequency of the high voltage appliedbetween the roll and the electrode is referred to as “dischargefrequency”. The corona discharge treatment is easily carried out underair atmosphere, but it may be done in a processing container filled withgas other than air or filled with air-contaminated gas while thecontainer is sealed or semi-sealed. Examples of the gas include nitrogengas, argon gas and oxygen gas.

[0269] The discharge frequency is normally in the range of 50 Hz to5,000 kHz, preferably in the range of 5 to several hundreds kHz. If itis too low, the discharge is so unstable that the resultant film hasmany pinholes. On the other hand, if it is too high, the treatment costsa lot because an apparatus for impedance matching must be usedadditionally.

[0270] For normally improving the wettability, the cellulose acetatefilm is subjected to corona discharge treatment preferably in an amountof 0.001 to 5 kV·A·minute/m², more preferably in an amount of 0.01 to 1kV·A·minute/m². The gap between the roll and the electrode is preferablyin the range of 0.5 to 2.5 mm, more preferably in the range of 1.0 to2.0 mm.

[0271] The glow discharge treatment comprises the steps of applying highvoltage between a pair of (or more) electrodes under low-pressured gasatmosphere, and placing or moving the cellulose acetate film in glowdischarge generated between the electrodes.

[0272] The gas pressure is normally in the range of 0.005 to 20 Torr,preferably in the range of 0.02 to 2 Torr. If it is too low, the surfacetreatment cannot give an effect. On the other hand, if it is too high,excess current flows to spark or to destroy the film. For causing thedischarge, the voltage is applied between a pair of (or more) metalplates or rods in a vacuum tank. The voltage depends upon the gas andits pressure, but is normally in the range of 500 to 5,000 V to causestable stationary glow discharge in the above pressure range. In orderto improve the adhesion, it is preferably in the range of 2,000 to 4,000V. The discharge frequency is generally in the range of 0 (directcurrent) to several thousands MHz, preferably in the range of 50 Hz to20 MHz. The cellulose acetate film is subjected to glow dischargetreatment preferably in an amount of 0.01 to 5 kV·A·minute/m², morepreferably in an amount of 0.15 to 1 kV·A·minute/m², to obtain desiredadhesion strength.

[0273] In the ultraviolet (UV) treatment, the cellulose acetate film isexposed to ultraviolet rays. If the film surface may be heated to about150° C. in consideration of film characters, a high pressure mercurylamp (main wavelength: 365 nm) is usable as a light source. If the filmmust be treated at a low temperature, a low pressure mercury lamp (mainwavelength: 254 nm) is preferably used. Other light sources such as highand low pressure mercury lamps of ozone-less type may be used. The moreamount of UV light the film is exposed to, the more the adhesion isimproved. However, if exposed to too much amount of UV light, the filmis colored and mechanically weakened. Accordingly, if the high pressuremercury lamp (main wavelength: 365 nm) is used, the exposed amount ispreferably in the range of 20 to 10,000 mJ/cm², more preferably in therange of 50 to 2,000 mJ/cm². If the low pressure mercury lamp (mainwavelength: 254 nm) is used, it is preferably in the range of 100 to10,000 mJ/cm², more preferably in the range of 300 to 1,500 mJ/cm².

[0274] (Optical Compensatory Sheet Comprising Optically AnisotropicLayer)

[0275] An optically anisotropic layer prepared from a liquid crystalcompound is provided on the cellulose acetate film to produce theoptical compensatory sheet of the invention. Preferably, an orientationlayer is provided between the cellulose acetate film and the opticallyanisotropic layer provided thereon. The orientation layer alignsmolecules of the liquid crystal compound in a certain direction, andhence it is indispensable for the invention. After the molecules arealigned with the orientation layer, they may be fixed with the alignmentmaintained. If so, since the orientation layer already accomplished itswork, the optical compensatory sheet does not need to comprise theorientation layer. In fact, the optically anisotropic layer containingthe aligned and fixed liquid crystal molecules can be alone transferred(without the orientation layer) onto the cellulose acetate film, toprepare an optical compensatory sheet,

[0276] (Orientation Layer)

[0277] The orientation layer has a function of giving an orientationdirection of the liquid crystal molecules. Preferred examples of theorientation layer include a layer of an organic compound (preferablypolymer) subjected to rubbing treatment, an obliquely deposited layer ofan inorganic compound, and a layer having micro grooves. Further, abuilt-up film formed according to Langmuir-Blodgett technique (LBtechnique) from ω-tricosanoic acid, dioctade-cyldimethylammoniumchlorideor methyl stearate can be used as the orientation layer. In addition, alayer prepared by orienting dielectric materials by application ofelectric field or magnetic field can be employed as the orientationlayer.

[0278] The orientation layer is preferably made of a polymer subjectedto rubbing treatment. As the polymer, polyvinyl alcohol is preferred.Particularly, denatured polyvinyl alcohol having hydrophobic groups ispreferred. The orientation layer can be prepared from only one polymer.However, for preparing the orientation layer, a layer made of twocrosslinked polymers is subjected to rubbing treatment. At least one ofthe two polymers is preferably crosslinkable by itself or with acrosslinking agent. The polymers which originally have functional groupsor to which functional groups are introduced are reacted with light,heat or pH variation to form the orientation layer; or otherwise linkinggroups are introduced by a reactive crosslinking agent into the polymersso that the polymers can be crosslinked to form the orientation layer.

[0279] In a normal process, a coating liquid containing the polymersand, if needed, the crosslinking agent is applied on the celluloseacetate film, and then heated to induce the crosslinking reaction. Thereaction may be caused at any stage from the step of coating the filmwith the coating liquid to the step of producing the resultant sheet.

[0280] In consideration of orientation of the liquid crystal molecules(in the optically anisotropic layer) on the orientation layer, thecrosslinking reaction is preferably caused sufficiently after themolecules are aligned.

[0281] Generally, the coating liquid is applied, heated and dried toform the orientation layer on the cellulose acetate film. In thatprocess, the liquid is preferably heated at such a low temperature thatthe molecules are fully crosslinked at stage of heating.

[0282] Polymers crosslinkable either by itself or with crosslinkingagents can be used. Some polymers are crosslinkable both by itself andwith crosslinking agents. Examples of the polymers include polymethylmethacrylate, acrylic acid/methacrylic acid copolymer,styrene/maleinimide copolymer, polyvinyl alcohol and denatured polyvinylalcohol, poly(N-methylolacrylamide), styrene/vinyltoluene copolymer,chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride,chlorinated polyolefin, polyester, polyimide, vinyl acetate/vinylchloride copolymer, ethylene/vinyl acetate copolymer, carboxymethylcellulose, polyethylene, polypropylene, polycarbonate, and organicsubstances such as silan coupling agents.

[0283] Preferred examples are water-soluble polymers such aspoly(N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinylalcohol and denatured polyvinyl alcohol. Gelatin, polyvinyl alcohol anddenatured polyvinyl alcohol are particularly preferred, and polyvinylalcohol and denatured polyvinyl alcohol are further preferred.

[0284] It is most preferred to use two kinds of polyvinyl alcohols ordenatured polyvinyl alcohols having different polymerization degrees.

[0285] The saponification degree of the polyvinyl alcohol is in therange of 70 to 100%, preferably in the range of 80 to 100%, morepreferably in the range of 85 to 95%. The polymerization degree ispreferably in the range of 100 to 3,000.

[0286] Examples of the denatured polyvinyl alcohol include polyvinylalcohols denatured by copolymerization, by chain transfer and by blockpolymerization. Examples of the denaturing group in the copolymerizationinclude COONa, Si(OX)₃, N(CH₃)₃.Cl, C₀H₁₉COO, SO₃Na and C₁₂H₂₅. Examplesof the denaturing group in the chain transfer include COONa, SH andC₁₂H₂₅. Examples of the denaturing group in the block polymerizationinclude COOH, CONH₂, COOR and C₆H₅.

[0287] Non-denatured or denatured polyvinyl alcohols havingsaponification degrees of 80 to 100% are preferred, and those havingsaponification degrees of 85 to 95% are further preferred.

[0288] The denatured polyvinyl alcohol is preferably a product ofreaction between polyvinyl alcohol and the compound represented by thefollowing formula. Hereinafter, such denatured polyvinyl alcohol isreferred to as “the particular denatured polyvinyl alcohol”.

[0289] in which R¹ is an alkyl group, an acryloylalkyl group, amethacryloylalkyl group or an epoxyalkyl group; W is a halogen atom, analkyl group or an alkoxy group; X is an atomic group required to form anactive ester, an acid anhydride or a acid halide; p is 0 or 1; and n isan integer of 0 to 4.

[0290] The denatured polyvinyl alcohol is more preferably a product ofreaction between polyvinyl alcohol and the compound represented by thefollowing formula:

[0291] in which X¹ is an atomic group required to form an active ester,an acid anhydride or a acid halide; and m is an integer of 2 to 24.

[0292] The polyvinyl alcohol reacted with the compound represented bythe above formulas are the aforementioned non-denatured polyvinylalcohols or polyvinyl alcohols denatured by copolymerization, by chaintransfer or by block polymerization. Preferred examples of theparticular denatured polyvinyl alcohol are described in Japanese PatentProvisional Publication No. 9(1997)-152509.

[0293] With respect to the polyvinyl alcohol, Japanese PatentProvisional Publication No. 8(1996)-338913 describes the synthesis, themeasurement of visible absorption spectrum and how to determine theamount of introduced denaturing groups.

[0294] Examples of the crosslinking agent include aldehydes, (e.g.,formaldehyde, glyoxal, glutaraldehyde), N-methylol compounds (e.g.,dimethylol urea, methyloldimethylhydantoin), dioxane derivatives (e.g.,2,3-dihydroxydioxane), compounds that works when the carboxylic group isactivated (e.g., carbenium, 2-naphthalenesulfonate,1,1-bispyrrolidino-1-chloropyridinium,1-morpholinocarbonyl-3-(sulfonatoaminomethyl), active vinyl compounds(e.g., 1,3,5-triacryloyl-hexahydro-s-triazine,bis-(vinylsulfone)methane,N,N′-methylenebis-[β-vinylsulfonyl]propionamide), active halogencompounds (e.g., 2,4-dichloro-6-hydroxy-s-triazine), isooxazoles anddialdehyde starch. Two or more crosslinking agents may be used incombination.

[0295] They are used together with preferably water-soluble polymer,more preferably polyvinyl alcohol or denatured polyvinyl alcohol(including the above particular polyvinyl alcohol). Reactive aldehydesare preferred, and glutaraldehyde is particularly preferred inconsideration of productivity.

[0296] The amount of the crosslinking agent is not particularlyrestricted. The more the crosslinking agent is added, the more thedurability against moisture is improved. However, if the amount ofcrosslinking agent is 50 wt. % or more per the amount of the polymer,the resultant orientation layer poorly aligns the molecules.Accordingly, the amount of crosslinking agent is preferably in the rangeof 0.1 to 20 wt. %, more preferably in the range of 0.5 to 15 wt. %based on the amount of the polymer. Even after the crosslinking reactionis completed, the obtained orientation layer contains non-reactedcrosslinking agent a little. The amount of the non-reacted crosslinkingagent remaining in the orientation layer is preferably not more than 1.0wt. %, more preferably not more than 0.5 wt. % based on the amount ofthe orientation layer. If the layer contains the non-reacted agent in anamount of more than 1.0 wt. %, the layer has poor durability. A liquidcrystal display comprising such orientation layer often suffers troublesof reticulation if used for a long time or left under hot and humidcondition.

[0297] The orientation layer can be formed by the steps of coating thecellulose acetate film with a coating liquid containing the abovepolymer and (if needed9 the crosslinking agent, heating to dry andcrosslink the applied polymer, and subjecting the formed layer torubbing treatment. The crosslinking reaction may be caused at any stepafter applying the coating liquid.

[0298] In the case where a water-soluble polymer such as polyvinylalcohol is used, the coating solution is preferably prepared from amixed solvent of water and an organic solvent having defoaming character(e.g., methanol). The ratio of water/methanol is normally in the rangeof 0:100 to 99:1, preferably in the range of 0:100 to 91:9. Because ofdefoaming character of the organic solvent, defects on the orientationlayer are remarkably decreased, and accordingly the opticallyanisotropic layer has an improved surface.

[0299] As the coating method, known methods such as spin coating, dipcoating, curtain coating, extrusion coating, bar coating and E typecoating can be adopted. The E type-coating method is particularlypreferred.

[0300] The thickness of the layer is preferably in the range of 0.1 to10 μm. The applied layer can be dried at a temperature of 20 to 110° C.For ensuring sufficient crosslinking, the temperature is preferably inthe range of 60 to 100° C., more preferably in the range of 80 to 100°C. The time for drying is in the range of 1 minute to 36 hours,preferably in the range of 5 minute to 30 minutes. The pH is alsopreferably adjusted at an optimal value according to the usedcrosslinking agent. If glutaraldehyde is used as the crosslinking agent,the pH is preferably in the range of 4.5 to 5.5, more preferably at 5.0.

[0301] The orientation layer is provided on the cellulose acetate filmor an undercoating layer. After the above-described polymer layer iscrosslinked, the surface of the layer is subjected to rubbing treatmentto form the orientation layer.

[0302] The rubbing treatment can be conducted in the manner adoptedwidely for aligning liquid crystal molecules of LCD. The surface of thelayer is rubbed with paper, cloth (gauze, felt, nylon, polyester) orrubber along a certain direction, to give the aligning function.Generally, the layer is rubbed several times with cloth on which fibershaving the same length and thickness are provided. The orientation layerdetermines the aligning direction of liquid crystal molecules providedthereon.

[0303] (Optically Anisotropic Layer)

[0304] In the invention, an optically anisotropic layer prepared from aliquid crystal compound is provided on the orientation layer formed onthe cellulose acetate film.

[0305] The-liquid crystal compound composing the optically anisotropiclayer may be a rod-like liquid crystal compound or a discotic one. Therod-like or discotic liquid crystal compound may have a low molecularweight or a high molecular weight. Further, a low molecular weightliquid crystal compound is crosslinked to become a compound that doesnot behave as liquid crystal. Such compound is also usable.

[0306] For preparing the optically anisotropic layer, a solutioncontaining the liquid crystal compound and other optional components(such as polymerization initiator) is applied on the orientation layer.

[0307] A solvent for the preparation of the solution preferably is anorganic solvent. Examples of the organic solvents include amides (e.g.,N,N-dimethylformamide), sulfoxides (e.g., dimethylsulfoxide),heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene,hexane), alkyl halides (e.g., chloroform, dichloromethane), esters(e.g., methyl acetate, butyl acetate), ketones (e.g., acetone, methylethyl ketone) and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane).Alkyl halides and ketones are preferred. Two or more organic solventscan be used in combination.

[0308] The solution can be coated according to a conventional coatingmethod such as a wire-bar coating method, an extrusion coating method, adirect gravure coating method, a reverse gravure coating method or a diecoating method.

[0309] The thickness of the optically anisotropic layer is preferably inthe range of 0.1 to 20 μm, more preferably in the range of 0.5 to 15 μm,most preferably in the range of 1 to 10 μm.

[0310] As the liquid crystal compound used in the invention, a discoticliquid crystal compound is preferably used.

[0311] (Rod-Like Liquid Crystal Compound)

[0312] Examples of the rod-like liquid crystal compound includeazomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic esters,phenyl esters of cyclohexanecarboxylates, cyanophenylcyclohexanes,cyano-substituted phenylpyrimidines, alkoxy-substitutedphenylpyrimidines, phenyldioxanes, tolanes, andalkenylcyclohexylbenzonitriles.

[0313] Metal complexes are also included in the rod-like liquid crystalcompounds. Further, a liquid crystal polymer in which the repeating unitcomprises a rod-like liquid crystal moiety is also usable as therod-like liquid crystal compound. On other words, the rod-like liquidcrystal compound may be combined with a (liquid crystal) polymer.

[0314] Descriptions of the rod-like liquid crystal compounds are foundin “Kagaku-Sosetsu, Ekisho no Kageku” (written in Japanese), vol.22(1994), Chapters 4, 7 and 11; and “Ekisho Devise Handbook” (written inJapanese), chapter 3.

[0315] The rod-like liquid crystal molecule preferably has abirefringent index of 0.001 to 0.7.

[0316] The rod-like liquid crystal molecule preferably has apolymerizable group (O) to fix the alignment.

[0317] Examples of the polymerizable group (O) are shown below.

[0318] The polymerizable group (O) preferably is an unsaturatedpolymerizable group (Q1 to Q7), an epoxy group (Q8) or an aziridinylgroup (Q9), more preferably is an unsaturated polymerizable group, andmost preferably is an ethylenically unsaturated group (Q1 to Q6).

[0319] The rod-like liquid crystal molecule preferably has an almostsymmetrical structure, and accordingly preferably has a polymerizablegroup at each end.

[0320] Examples of the rod-like liquid crystal molecule are shown below.

[0321] The optically anisotropic layer is prepared by coating theorientation layer with a liquid crystal composition (coating solution)containing the rod-like liquid crystal compound and other optionalcomponents such as polymerization initiator and additives (e.g.,plasticizer, monomer, surface active agent, cellulose acetate,1,3,5-triazine, chiral agent).

[0322] (Discotic Liquid Crystal Compound)

[0323] The discotic molecules give large birefringence and have variousalignment forms, and accordingly an optical compensatory sheet obtainedfrom the discotic molecules has a specific optical characteristic thatcannot be obtained from the conventional stretched birefringent film.The optical compensatory sheet comprising discotic molecules isdescribed in Japanese Patent Provisional Publication No. 6(1994)-214116,U.S. Pat. Nos. 5,583,679, 5,646,703 and German Patent Publication No.3,911,620A1.

[0324] Examples of the discotic liquid crystal compound include benzenederivatives described in C. Destrade et al., Mol. Cryst. vol. 71, pp.111, (1981); truxene derivatives described in C. Destrade et al., MolCryst. vol. 122, pp. 141. (1985), Physics lett. A, vol. 78, pp. 82,(1990); cyclohexane derivatives described in B. Kohn et al., Angew.Chem. vol. 96, pp. 70, (1984); and macrocyclic compounds ofazacrown-type or phenylacetylene-type described in J. M. Lehn et al., J.Chem. Commun. pp. 1794, (1985), and J. Zhang et al., J. Am. Chem. Soc.vol. 116, pp.2655, (1994).

[0325] The discotic compound has a structure in which the discoticstructure unit is located at the center as a parent core and furtherstraight chain groups such as alkyl, alkoxy and substituted benzoyl areradially substituted. The discotic compound generally has the propertiesof liquid crystal, and hence includes a compound generally calleddiscotic liquid crystal. As the discotic liquid compounds, any compoundcan be used so long as it has negative uniaxial property and orientationproperty. Substance derived from the discotic compound is not always theabove-described compound. For example, the low molecular weight discoticliquid crystal compound having a thermo- or photo-reactive group ispolymerized by heat or light to form a polymer that does not behave asliquid crystal. Such polymer can be also used in the invention.Preferred examples of the discotic liquid crystal compound are describedin Japanese Patent Provisional Publication No. 8(1996)-50206. JapanesePatent Provisional Publication No. 8(1996)-27284 describespolymerization of the discotic liquid crystal compound.

[0326] A polymerizable group should be bound to a discotic core of thediscotic compound to cause the polymerization reaction of the compound.However, if the polymerizable group is directly bound to the discoticcore, it is difficult to keep the alignment at the polymerizationreaction. Therefore, a linking group is introduced between the discoticcore and the polymerizable group. Accordingly, the discotic compoundhaving a polymerizable group preferably is a compound represented by thefollowing formula (III).

D(-L-P)_(n)  (III)

[0327] in which D is a discotic core; L is a divalent linking group; Pis a polymerizable group; and n is an integer of 4 to 12.

[0328] Examples of the discotic cores (D) are shown below. In theexamples, LP (or PL) means the combination of the divalent linking group(L) and the polymerizable group (P).

[0329] In the formula (III), the divalent linking group (L) preferablyis selected from the group consisting of an alkylene group, analkenylene group, an arylene group, —CO, —NH—, —O—, —S— and combinationsthereof. L more preferably is a divalent linking group comprising atleast two divalent groups selected from the group consisting of analkylene group, an arylene group, —CO—, —NH—, —O— and —S—. L morepreferably is a divalent linking group comprising at least two divalentgroups selected from the group consisting of an alkylene group, anarylene group, —CO— and —O—. The alkylene group preferably has 1 to 12carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms.The arylene group preferably has 6 to 10 carbon atoms.

[0330] Examples of the divalent linking groups (L) are shown below. Inthe examples, the left side is attached to the discotic core (D), andthe right side is attached to the polymerizable group (P). The AL meansan alkylene group or an alkenylene group. The AR means an arylene group.The alkylene group, the alkenylene group and the arylene group may havea substituent group (e.g., an alkyl group).

[0331] L1: -AL-CO—O-AL-

[0332] L2: -AL-CO—O-AL-O—

[0333] L3: -AL-CO—O-AL-O-AL

[0334] L4: -AL-CO—O-AL-O—CO—

[0335] L5: —CO-AR-O-AL-

[0336] L6: —CO-AR-O-AL-O—

[0337] L7: —CO-AR-O-AL-O—CO—

[0338] L8: —CO—NH-AL-

[0339] L9: —NH-AL-O—

[0340] L10: —NH-AL-O—CO—

[0341] L11: —O-AL-

[0342] L12: —O-AL-O—

[0343] L13: —O-AL-O—CO—

[0344] L14: —O-AL-O—CO—NH-AL-

[0345] L15: —O-AL-S-AL-

[0346] L16: —O—CO-AR-O-AL-CO—

[0347] L17: —O—CO-AR-O-AL-O—CO—

[0348] L18: —O—CO-AR-O-AL-O-AL-O—CO—

[0349] L19: —O—CO-AR-O-AL-O-AL-O-AL-O—CO—

[0350] L20: —S-AL-

[0351] L21: —S-AL-O—

[0352] L22: —S-AL-O—CO—

[0353] L23: —S-AL-S-AL-

[0354] L24: —S-AR-AL-

[0355] The polymerizable group (P) is determined according to thepolymerization reaction. Examples of the polymerizable groups (P) areshown below.

[0356] The polymerizable group (P) preferably is an unsaturatedpolymerizable group (P1, P2, P3, P7, P8, P15, P16, P17) or an epoxygroup (P6, P18), more preferably is an unsaturated polymerizable group,and most preferably is an ethylenically unsaturated group (P1, P7, P8,P15, P16, P17). In the formula (I), n is an integer of 4 to 12, which isdetermined according to the chemical structure of the discotic core (D).The 4 to 12 combinations of L and P can be different from each other.However, the combinations are preferably identical. The discotic liquidcrystal compound is described in Japanese Patent Provisional PublicationNos. 7(1995)-281028, 7(1995)-306317, 8(1996)-50206, 9(1997)-104656,9(1997)-104866 and 9(1997)-11240.

[0357] If the discotic compound is used, the optically anisotropic layeris a negative birefringent layer. In the optically anisotropic layer,discotic structure units of the discotic compound preferably have planesinclined from a plane of the cellulose acetate film at an angle varyingin (along) the direction of depth of the layer.

[0358] The above-described angle (inclined angle) of the plane ofdiscotic structure unit generally increases or decreases with increaseof distance in the direction of depth from the bottom of the opticallyanisotropic layer. The inclined angle preferably increases with increaseof the distance. Further, examples of variation of the inclined angleinclude continuous increase, continuous decrease, intermittent increase,intermittent decrease, variation containing continuous increase anddecrease, and intermittent variation containing increase or decrease.The intermittent variation contains an area where the inclined angledoes not vary in the course of the thickness direction of the layer. Theinclined angle preferably totally increases or decreases in the layer,even if it does not vary in the course. The inclined angle morepreferably increases totally, and it is particularly preferred toincrease continuously. The inclined angle of the discotic unit on thesupport side can be generally controlled by selecting the discoticcompound or materials of the orientation layer, or by selecting methodsfor the rubbing treatment. The discotic compound or other compounds usedtogether with the discotic compound can be selected to control theinclined angle of the discotic unit on the surface side (air side).Examples of the compounds used together with the discotic compoundinclude a plasticizer, a surface active agent, a polymerizable monomerand a polymer. Further, the extent of variation of the inclined anglecan be also controlled by the above selection.

[0359] Any compound can be employed as the plasticizer, the surfaceactive agent and the polymerizable monomer, so long as it is compatiblewith the discotic compound and it gives variation of the inclined angleor dose not inhibit the discotic compound molecules from aligning.Preferred is polymerizable monomer (e.g., compounds having a vinyl,vinyloxy, acryloyl or methacryloyl group). Those compounds arepreferably used in the amount of 1 to 50 wt. % (especially 5 to 30 wt.%) based on the amount of the discotic compound.

[0360] Any polymer can be used together with the discotic liquid crystalcompound, so long as it is compatible with the discotic compound and itgives variation of the inclined angle. The polymer is, for example,cellulose ester. Preferred examples of the cellulose acetate includecellulose acetate, cellulose acetatepropionate, hydrocypropyl-cellulose,and cellulose acetatebutylate. In order not to prevent molecules of thediscotic compound from aligning, the amount of the polymer is generallyin the range of 0.1 to 10 wt. %, preferably in the range of 0.1 to 8 wt.%, more preferably in the range of 0.1 to 5 wt. % based on the amount ofthe discotic compound.

[0361] The optically anisotropic layer can be generally prepared by thesteps of coating the orientation layer with a solution of the discoticcompound and other compounds dissolved in a solvent, drying, heating toa temperature for forming a discotic nematic phase, and cooling with theoriented condition (discotic nematic phase) kept. Otherwise, the layercan be prepared by the steps of coating the orientation layer with asolution of the discotic compound and other compounds (e.g.,polymerizable monomer, photo-polymerization initiator) dissolved in asolvent, drying, heating to a temperature for forming a discotic nematicphase, polymerizing the heated layer (e.g., by radiation of UV light)and cooling. The transition temperature from discotic nematic phase tosolid phase is preferably in the range of 70 to 300° C., especially 70to 170° C.

[0362] (Fixation of Alignment of Liquid Crystal Compound)

[0363] The aligned discotic liquid crystal molecules can be fixed withthe alignment maintained. The discotic liquid crystal molecules arefixed preferably by a polymerization reaction. The polymerizationreaction can be classified into a thermal reaction with a thermalpolymerization initiator and a photo reaction with a photopolymerization initiator. A photo polymerization reaction is preferred.

[0364] Examples of the photo polymerization initiators includeα-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661, 2,367,670),acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbonsubstituted acyloin compounds (described in U.S. Pat. No. 2,722,512),polycyclic quinone compounds (described in U.S. Pat. Nos. 2,951,758,3,046,127), combinations of triarylimidazoles and p-aminophenyl ketones(described in U.S. Pat. No. 3,549,367), acridine or phenazine compounds(described in Japanese Patent Provisional Publication No.60(1985)-105667 and U.S. Pat. No. 4,239,850) and oxadiazole compounds(described in U.S. Pat. No. 4,212,970).

[0365] The amount of the photo polymerization initiator is preferably inthe range of 0.01 to 20 wt. %, and more preferably in the range of 0.5to 5 wt. % based on the solid content of the coating solution.

[0366] The light irradiation for the photo polymerization is preferablyconducted with ultraviolet rays.

[0367] The exposure energy is preferably in the range of 20 to 50,000mJ/cm², more preferably in the range of 20 to 5,000 mJ/cm², mostpreferably in the range of 100 to 800 mJ/cm². The light irradiation canbe conducted while the layer is heated to accelerate the photopolymerization reaction. The protective layer may be provided on theoptically anisotropic layer.

[0368] (Polarizing Plate)

[0369] The polarizing plate comprises two transparent protective filmsand a polarizing membrane provided between the films. The opticalcompensatory sheet comprising the cellulose acetate film or thecellulose acetate film having the optically anisotropic layer providedthereon can be used as one of the protective films. A normal celluloseacetate film can be used as the other protective film.

[0370] Examples of the polarizing membrane include an iodine polarizingmembrane, a polyene polarizing membrane and a dichromatic dye polarizingmembrane. The iodine polarizing membrane and the dye polarizing membraneare generally prepared from polyvinyl alcohol films. The transmissionaxis of the polarizing membrane is placed perpendicularly to thestretching direction of the film.

[0371] The slow axis of the cellulose acetate film may be essentiallyparallel or perpendicularly to the transmission axis of the polarizingmembrane.

[0372] It has been found that the moisture-permeability of theprotective film is important for production of the polarizing plate. Inproducing the polarizing plate, the polarizing membrane and theprotective film are laminated with an aqueous adhesive, and then thesolvent of the adhesive is diffused into the film to dry. The higherpermeability the film has, the more rapidly it is dried. Accordingly,the productivity of the polarizing plate is improved. However, if thepermeability is too high, the outer moisture is liable to come into themembrane to impair polarizability if the liquid crystal display is usedunder humid condition.

[0373] The moisture-permeability depends upon various conditions such asthickness, free volume, and hydrophilicity (hydrophobicity) of thepolymer film (and the polymerizable liquid crystal compound).

[0374] In the case where the optical compensatory sheet is used as theprotective film of the polarizing plate, the compensatory sheet has amoisture-permeability preferably in the range of 100 to 1,000 (g/m²)/24hours, more preferably in the range of 300 to 700 (g/m²)/24 hours.

[0375] In the film forming process, conditions and procedures such asrip flow, line speed, stretching and/or compressing are adequatelyselected to control the thickness of the compensatory sheet. Since themoisture-permeability depends upon the materials, the thickness iscontrolled so that the preferred permeability can be obtained.

[0376] Also in the film forming process, drying conditions such as timeand temperature are suitably determined to control the free volume ofthe optical compensatory sheet. Since the moisture-permeability dependsupon the materials, the free volume is controlled so that the preferredpermeability can be obtained.

[0377] The hydrophilicity (hydrophobicity) of the transparent base filmcan be controlled with additives. If hydrophilic additives are containedin the free volume, the permeability is increased. If hydrophobicadditives are added, the permeability is decreased.

[0378] The moisture-permeability can be thus controlled, and thereby thepolarizing plate having optical compensatory function can be produced atsmall cost with high productivity.

[0379] (Circularly Polarizing Plate)

[0380] The λ/4 plate of the invention (optical compensatory sheetcomprising the cellulose acetate film) and the polarizing membrane arelaminated so that the slow axis in the plane of the λ/4 plate may beplaced essentially at the angle of 45° to the transmission axis of themembrane, to produce a circularly polarizing plate. The term “placedessentially at the angle of 45°” means that the angle between the slowaxis of λ/4 plate and the transmission axis of membrane is in the rangeof 40° to 50°. The angle is preferably in the range of 41° to 490, morepreferably in the range of 420 to 48°, further preferably in the rangeof 43° to 47°, most preferably in the range of 440 to 460. On the backsurface of the polarizing membrane (surface not facing to the λ/4plate), a transparent protective film is preferably provided. As thetransparent protective film, a conventional cellulose acetate film maybe used.

[0381] (Liquid Crystal Display)

[0382] The aforementioned optical compensatory sheet or the polarizingplate in which the compensatory sheet and the polarizing membrane arelaminated is particularly advantageously used in a liquid crystaldisplay of transmission type or reflection type. The retardation valuesof the optically anisotropic cellulose acetate film are determinedaccording to the aimed characters of liquid crystal display.

[0383] (Liquid Crystal Display of Transmission Type)

[0384] A liquid crystal display of transmission type comprises a pair ofpolarizing plates and a liquid crystal cell placed between them. Thepolarizing plate comprises a pair of transparent protective films and apolarizing membrane placed between them. The liquid crystal cellcomprises a pair of substrates and liquid crystal provided between them.

[0385] In the case where the optical compensatory sheet of the inventionis used in the liquid crystal display, the compensatory sheet is placedbetween the cell and one or each of the polarizing plates.

[0386] In the case where the polarizing plate of the invention is usedin the liquid crystal display, it may be used as one of the two plates.The plates on both sides of the cell may be the polarizing plates of theinvention. The polarizing plate of the invention is placed so that theoptical compensatory sheet (which serves as a protective film of thepolarizing plate) may face to the liquid crystal cell.

[0387] The liquid crystal cell works preferably according to VA mode(including MVA), OCB mode or TN mode.

[0388] The liquid crystal cell of OCB mode is a liquid crystal cell ofbend alignment mode in which rod-like liquid crystal molecules in upperpart and ones in lower part are aligned essentially in reverse(symmetrically). A liquid crystal display having the liquid crystal cellof bend alignment mode is disclosed in U.S. Pat. Nos. 4,583,825 and5,410,422. Since rod-like liquid crystal molecules in upper part andones in lower part are symmetrically aligned, the liquid crystal cell ofbend alignment mode has self-optical compensatory function. Therefore,this mode is referred to as OCB (optically compensatory bend) mode. Theliquid crystal display of bend alignment mode has an advantage ofresponding rapidly.

[0389] In a liquid crystal cell of VA mode, rod-like liquid crystalmolecules are essentially vertically aligned while voltage is notapplied. The liquid crystal cell of VA mode include some types: (1) aliquid crystal cell of VA mode in a narrow sense (described in JapanesePatent Provisional Publication No. 2(1990)-176625 and Japanese PatentPublication No. 7(1995)-69536), in which rod-like liquid crystalmolecules are essentially vertically aligned while voltage is notapplied, and the molecules are essentially horizontally aligned whilevoltage is applied; (2) a liquid crystal cell of MVA mode (described inSID97, Digest of tech. Papers, 28(1997), 845; SID99, Digest of tech.Papers, 30(1999), 206; and Japanese Patent Provisional Publication No.11(1999)-258605), in which the VA mode is modified to be multi-domaintype so as to enlarge the viewing angle), a cell of SURVAIVAL mode(described in “monthly Display (written in Japanese)”, 6(1999), No. 3,pp. 14), a cell of PVA mode (described in Asia Display 98, Proc. of the18^(th) Inter. Display res. Conf., Papers, (1998), pp. 383), a cell ofPara-A mode (presented in LCD/PDP International '99), a cell of DDVAmode (described in SID98, Digest of tech. Papers, 29(1998), 838), a cellof EOC mode (described in SID98, Digest of tech. Papers, 29(1998), 319),a cell of PSHA mode (described in SID98, Digest of tech. Papers,29(1998), 1081), a cell of RFFMH mode (described in Asia Display 98,Proc. of the 18^(th) Inter. Display res. Conf., Papers, (1998), pp.375), and a cell of HMD mode (described in SID98, Digest of tech.Papers, 29(1998), 702); and (3) a liquid crystal cell of n-ASM mode(described in IWD '98, Proc. of the 5^(th) Inter. Display WorkshopPapers, (1998), pp. 143), in which rod-like liquid crystal molecules areessentially vertically aligned while voltage is not applied, and themolecules are essentially oriented in twisted multi-domain alignmentwhile voltage is applied.

[0390] In a liquid crystal cell of TN mode, rod-like liquid crystalmolecules are essentially horizontally aligned while voltage is notapplied, and oriented in a twisted alignment with a twisted angle of 60to 120°. The liquid crystal cell of TN mode is widely used in color TFTliquid crystal displays, and hence is described in many publications.

[0391] (Liquid Crystal Display of Reflection Type)

[0392]FIG. 1 schematically shows the basic structure of a liquid crystaldisplay of reflection type.

[0393] The display shown in FIG. 1 comprises a lower substrate (1), areflective electrode (2), a lower orientation layer (3), a liquidcrystal layer (4), an upper orientation layer (5), a transparentelectrode (6), an upper substrate (7), a λ/4 plate (8) and a polarizingmembrane (9), piled up in this order.

[0394] A combination of the lower substrate (1) and the reflectiveelectrode (2) constitutes a reflection board. A combination of the lowerorientation layer (3) to the upper orientation layer (5) constitutes aliquid crystal cell. The λ/4 plate (8) may be placed at any positionbetween the reflection board and the polarizing membrane (9).

[0395] For displaying a color image, a color filter layer isadditionally provided. The color filter is preferably placed between thereflective electrode (2) and the lower orientation layer (3), or betweenthe upper orientation layer (5) and the transparent electrode (6).

[0396] In place of the reflective electrode (2), a transparent electrodemay be used in combination with a reflection board. The reflection boardis preferably a metal board or a semi-transparent reflection board. Ifthe reflection board has a smooth surface, rays parallel to the normalof the surface are often predominantly reflected to give a small viewingangle. Therefore, the surface of the reflection board may be made rugged(as described in Japanese Patent No. 276,620). Otherwise, alight-diffusing film may be provided on one surface (cell side or airside) of the polarizing membrane.

[0397] The liquid crystal cell is preferably TN (twisted nematic) mode,STN (supper twisted nematic) mode, or HAN (hybrid aligned nematic) mode.

[0398] The liquid crystal cell of TN mode has a twist angle preferablyin the range of 40 to 100°, more preferably in the range of 50 to 90°,most preferably in the range of 60 to 80°. The product (Δn·d) ofrefractive anisotropy (Δn) and thickness (d) of the liquid crystal layeris preferably in the range of 0.1 to 0.5 μm, more preferably in therange of 0.2 to 0.4 μm.

[0399] The liquid crystal cell of STN mode has a twist angle preferablyin the range of 180 to 360°, more preferably in the range of 220 to2700. The product (Δn·d) of refractive anisotropy (Δn) and thickness (d)of the liquid crystal layer is preferably in the range of 0.3 to 1.2 μm,more preferably in the range of 0.5 to 1.0 μm.

[0400] In the liquid crystal cell of HAN mode, it is preferred thatliquid crystal molecules be essentially vertically aligned on onesubstrate and that the pre-tilt angle on the other substrate be in therange of 0 to 45°. The product (Δn·d) of refractive anisotropy (Δn) andthickness (d) of the liquid crystal layer is preferably in the range of0.1 to 1.0 μm, more preferably in the range of 0.3 to 0.8 μm. Thesubstrate on which the liquid crystal molecules are vertically alignedmay be on the transparent electrode side or on the opposite side.

[0401] The liquid crystal display of reflection type may be designednormally white mode (in which a bright or dark image is displayed whenthe applied voltage is low or high, respectively) or normally black mode(in which a dark or bright image is displayed when the applied voltageis low or high, respectively). The normally white mode is preferred.

[0402] (Guest-Host Liquid Crystal Display of Reflection Type)

[0403]FIG. 2 is a sectional view illustrating a representativeembodiment of the guest-host liquid crystal display of reflection type.

[0404] The display shown in FIG. 2 comprises a lower substrate (11), anorganic insulating layer (12), a metal reflection board (13), a λ/4plate (14), a lower transparent electrode (15), a lower orientationlayer (16), a liquid crystal layer (17), an upper orientation layer(18), an upper transparent electrode (19), a light-diffusing layer (20),an upper substrate (21) and an anti-reflection layer (22), piled up inthis order.

[0405] The lower substrate (11) and the upper substrate (21) are made ofglass or plastics. A TFT (23) is provided between the lower substrate(11) and the organic insulating layer (12).

[0406] The liquid crystal layer (17) contains a mixture of liquidcrystal and dichromatic dye. For forming the liquid crystal layer, themixture is injected into the cell gap formed with spacers (24).

[0407] Instead of providing the light-diffusing layer (20), the metalreflection board (13) may be made rugged so that the board (13) canserve as the diffusing layer.

[0408] The anti-reflection layer (22) preferably has an ant-glarefunction as well as the anti-reflection function.

[0409]FIG. 3 is a sectional view illustrating another representativeembodiment of the guest-host liquid crystal display of reflection type.

[0410] The display shown in FIG. 3 comprises a lower substrate (31), anorganic insulating layer (32), a cholesteric color reflection board(33), a λ/4 plate (34), a lower transparent electrode (35), a lowerorientation layer (36), a liquid crystal layer (37), an upperorientation layer (38), an upper transparent electrode (39), an uppersubstrate (41) and an anti-reflection layer (42), piled up in thisorder.

[0411] The lower substrate (31) and the upper substrate (41) are made ofglass or plastics. A TFT (43) is provided between the lower substrate(31) and the organic insulating layer (32).

[0412] The λ/4 plate (34) may serve as the diffusing layer.

[0413] The liquid crystal layer (37) contains a mixture of liquidcrystal and dichromatic dye. For forming the liquid crystal layer, themixture is injected into the cell gap formed with spacers (44).

[0414] A black matrix is provided between the upper transparentelectrode (39) and the upper substrate (41).

[0415] The anti-reflection layer (42) preferably has an ant-glarefunction as well as the anti-reflection function.

[0416] The λ/4 plate according to the invention can be used as the λ/4plate (8) in the display of reflection type shown in FIG. 1, that (24)in the guest-host display of reflection type shown in FIG. 2, or that(34) in the guest-host display of reflection type shown in FIG. 3.

[0417] The guest-host liquid crystal display of reflection type equippedwith the λ/4 plate is described in Japanese Patent ProvisionalPublication Nos. 6(1994)-222350, 8(1996)-36174, 10(1998)-268300,10(1998)-292175, 10(1998)-293301, 10(1998)-311976, 10(1998)-319442,10(1998)-325953, 10(1998)-333138 and 11(1999)-38410.

[0418] The λ/4 plate of the invention can be used in the guest-hostliquid crystal displays of reflection type described in the abovepublications.

[0419] (Liquid Crystal Display of Bend Alignment Mode)

[0420] The optical compensatory sheet having the optically anisotropiclayer of the invention is preferably used in a liquid crystal display ofbend alignment mode. The display of bend alignment mode equipped withthe compensatory sheet is described below in detail.

[0421]FIG. 4 is a sectional view schematically illustrating alignment ofliquid crystal molecules in a liquid crystal cell of bend alignmentmode.

[0422] As shown in FIG. 4, the cell of bend alignment mode comprises anupper substrate (114 a), a lower substrate (114 b), and a liquid crystalcompound (111) provided between them. The liquid crystal compound (111)used in the cell of bend alignment mode generally has a positivedielectric anisotropy. The upper and lower substrates (114 a, 114 b)have orientation layers (112 a, 112 b) and electrode layers (113 a, 113b), respectively. The orientation layers align rod-like liquid crystalmolecules (111 a to 111 j). The direction indicated by RD is the rubbingdirection of orientation layer. The electrode layers have a function ofapplying a voltage to the rod-like liquid crystal molecules (111 a to111 j).

[0423]FIG. 4 (off) shows the alignment of rod-like liquid crystalmolecules when a low voltage is applied to the liquid crystal cell ofbend alignment mode. In that cell, the rod-like liquid crystal molecules(111 a to 111 e) on the side of the upper substrate (114 a) and those(111 f to 111 j) on the side of the lower substrate (114 b) are alignedessentially in reverse (symmetrically). The molecules (111 a, 111 b, 111i, 111 j) near the substrates (114 a, 114 b) are almost horizontallyaligned, and those (111 d to 111 g) at the central part in the cell arealmost vertically aligned.

[0424]FIG. 4 (on) shows the alignment of rod-like liquid crystalmolecules when a high voltage is applied. In that cell, the molecules(111 a, 111 j) near the substrates (114 a, 114 b) are still almosthorizontally aligned, and those (111 e, 111 f) at the central part arealso. still almost vertically aligned. In contrast, the molecules (111b, 111 c, 111 d, 111 g, 111 h, 111 i) in the area between the substrateand the center of the cell are raised as compared with those when a lowvoltage is applied (off-state). However, even in on-state, the molecules(111 a to 111 e) on the side of the upper substrate (114 a) and those(111 f to 111 j) on the side of the lower substrate (114 b) are stillaligned essentially in reverse (symmetrically).

[0425]FIG. 5 schematically shows an elliptically polarizing plateaccording to the invention.

[0426] As shown in FIG. 5, an elliptically polarizing plate is a layeredcomposition comprising a first optically anisotropic layer (131)containing discotic compound (131 a to 131 e), a second opticallyanisotropic layer (133) having at least one cellulose acetate film, anda polarizing membrane (134). The elliptically polarizing plate in FIG. 5further comprises an orientation layer (132) between the first opticallyanisotropic layer (131) and the second optically anisotropic layer(133).

[0427] The discotic compound (131 a to 131 e) in the first opticallyanisotropic layer (131) is a planar molecule. Each molecule of thediscotic compound has only one plane, namely a disc plane. The discplane is inclined from the surface of the second optically anisotropiclayer (133). The angle between the disc plane and the second opticallyanisotropic layer (the inclined angle) increases with increase ofdistance between the molecule and the orientation layer. The averageinclined angle is preferably in the range of 15 to 50°. The ellipticallypolarizing plate (shown in FIG. 5) in which the molecules have varyinginclined angles can remarkably improve the viewing angle. In addition,it can prevent the displayed image from tone inversion, tone fluctuationand undesired coloring.

[0428] The average direction (PL) obtained by projecting normal (NL) ofthe disc plane of the discotic molecule (131 a to 131 e) onto the secondoptically anisotropic layer (133) is anti-parallel to the rubbingdirection (RD) of the orientation layer (132).

[0429] In the invention, the average direction (PL) obtained byprojecting normal of the disc plane of the discotic molecule onto thetransparent support is positioned essentially at the angle of 45° to theslow axis (SA) in the plane of the second optically anisotropic layer(133). In order to produce such elliptically polarizing plate, therubbing direction (RD) of the orientation layer (132) is made to beessentially at the angle of 45° to the slow axis (SA) of the secondoptically anisotropic layer (133).

[0430] Further, in the invention, the transparent support and thepolarizing membrane are placed so that the transmission axis (TA) in theplane of the polarizing membrane (134) may be essentially parallel orperpendicular to the slow axis (SA) in the plane of the second opticallyanisotropic layer (133). In the elliptically polarizing plate shown inFIG. 5, a transparent support is placed so that the SA may be parallelto the TA. In principle, the slow axis (SA) in the plane of thetransparent support (133) corresponds to the stretching direction of thesecond optically anisotropic layer. Further, in principle, thetransmission axis (TA) in the plane of the polarizing membrane (134) isperpendicular to the stretching direction of the polarizing membrane.

[0431]FIG. 6 schematically shows a liquid crystal display of bendalignment mode according to the invention.

[0432] The liquid crystal display shown in FIG. 6 comprises a pair ofelliptically polarizing plates (131A to 134A, and 131B to 134B), aliquid crystal cell of bend alignment mode (110) provided between theplates, and backlight (BL).

[0433] The cell of bend alignment mode (110) corresponds to the liquidcrystal cell shown in FIG. 4. The directions (RD2, RD3) of rubbingtreatment applied on the upper and lower substrates of the cell (110),respectively, are the same (parallel to each other).

[0434] Each elliptically polarizing plate consists of a first opticallyanisotropic layer (131A, 131B), a second optically anisotropic layer(133A, 133B) and a polarizing membrane (134A, 134B), piled up in thisorder from the liquid crystal cell (110) side. Each rubbing direction(RD1, RD4) for aligning the discotic compound in the first opticallyanisotropic layer (131A, 131B) is anti-parallel to the rubbing direction(RD2, RD3) of the cell substrate opposite to the layer. The rubbingdirection (RD1, RD4) is also anti-parallel to the average directionobtained by projecting normal of the disc plane of the discotic compoundonto the transparent support. The slow axis (SA1, SA2) in the plane ofthe second optically anisotropic layer (133A, 133B) and the transmissionaxis (TA1, TA2) in the plane of the polarizing membrane are essentiallyat the angle of 45° to the rubbing direction (RD1, RD4) in the sameplane. The two polarizing membranes (134A, 134B) are placed so that thetransmission axis (TA1, TA2) in the plane may be perpendicularly crossed(may be in cross-Nicol position).

[0435]FIG. 7 schematically shows mechanism of optical compensation in aliquid crystal display of bend alignment mode.

[0436] As shown in FIG. 7, in the liquid crystal display of theinvention, the liquid crystal cell of bend alignment mode (110) isoptically compensated with the optically anisotropic layers 1 (131A,131B) and the optically anisotropic layers 2 (133A, 133B) incombination.

[0437] The rubbing direction (RD1, RD4) for aligning the discoticcompound in the first optically anisotropic layer (131A, 131B) isanti-parallel to the rubbing direction (RD2, RD3) of the cell, and henceeach discotic molecule in the optically anisotropic layers 1 (131A,131B) can correspond to each liquid crystal molecule in the cell (110)of bend alignment mode. (The correspondences are schematically indicatedby a to c, and e to g in FIG. 7.) The optically anisotropic layers 2(133A, 133B) also correspond to the liquid crystal molecules essentiallyvertically aligned in the central area of the cell (110). (Thesecorrespondences are schematically indicated by d and h in FIG. 7.) InFIG. 7, the-ellipse in each second optically anisotropic layer (133A,133B) represents a refractive ellipsoid derived from the opticalanisotropy.

[0438]FIG. 8 schematically shows various embodiments of the ellipticallypolarizing plate.

[0439]FIG. 8(a 1) shows the simplest elliptically polarizing plate shownin FIG. 5. The embodiment of FIG. 8(a 1) comprises a first opticallyanisotropic layer (131), a second optically anisotropic layer (133) anda polarizing membrane (134), piled up in this order. The rubbingdirection (RD) for aligning the discotic compound is essentially at theangle of 45° to the slow axis (SA) of the second optically anisotropiclayer (133), and the slow axis (SA) of the second optically anisotropiclayer (133) is essentially parallel to the transmission axis (TA) of thepolarizing membrane (134).

[0440] The embodiment of FIG. 8(a 2) also comprises a first opticallyanisotropic layer (131), a second optically anisotropic layer (133) anda polarizing membrane (134), piled up in this order. The rubbingdirection (RD) for aligning the discotic compound is essentially at theangle of 45° to the slow axis (SA) of the second optically anisotropiclayer (133), and the slow axis (SA) of the second optically anisotropiclayer (133) is essentially perpendicular to the transmission axis (TA)of the polarizing membrane (134).

[0441] The embodiment of FIG. 8(a 3) has a second optically anisotropiclayer consisting of two sub-layers (133 a, 133 b). In that embodiment,at least one anisotropic sub-layer 2 (133 b, in FIG. 8a 3) is placed atthe position satisfying the aforementioned condition. Namely, therubbing direction (RD) for aligning the discotic compound is essentiallyat the angle of 45° to the slow axis (SA2) of the above opticallyanisotropic sub-layer 2 (133 b), and that slow axis (SA2) is essentiallyparallel to the transmission axis (TA) of the polarizing membrane (134).The other anisotropic sub-layer 2 (133 a) is, as a conventional one,placed so that the slow axis (SA1) may be essentially parallel to therubbing direction (RD).

[0442] The embodiment of FIG. 8(a 4) has a second optically anisotropiclayer consisting of two sub-layers (133 a, 133 b) placed at thepositions satisfying the aforementioned condition with the firstoptically anisotropic layer (131) and the polarizing membrane (134).Namely, the rubbing direction (RD) for aligning the discotic compound isessentially at the angle of 45° to each of the slow axes (SA1, SA2) ofthe optically anisotropic sub-layers 2 (133 a, 133 b), and each of theslow axes (SA1, SA2) is essentially parallel to the transmission axis(TA) of the polarizing membrane (134).

[0443] The embodiment of FIG. 8(a 5) also has a second opticallyanisotropic layer consisting of two sub-layers (133 a, 133 b) placed atthe positions satisfying the aforementioned condition with the firstoptically anisotropic layer (131) and the polarizing membrane (134).Namely, the rubbing direction (RD) for aligning the discotic compound isessentially at the angle of 45° to each of the slow axes (SA1, SA2) ofthe optically anisotropic sub-layers 2 (133 a, 133 b). The slow axis(SAl) of the optically anisotropic sub-layer 2 (133 a) near the firstoptically anisotropic layer (131) is essentially perpendicular to thetransmission axis (TA) of the polarizing membrane (134). The slow axis(SA2) of the optically anisotropic sub-layer 2 (133 b) near thepolarizing membrane (134) is essentially parallel to the transmissionaxis (TA) of the polarizing membrane (134).

[0444]FIG. 9 schematically shows various other embodiments of theelliptically polarizing plate.

[0445] The embodiment of FIG. 9(b 1) comprises a second opticallyanisotropic layer (133), a first optically anisotropic layer (131) and apolarizing membrane (134), piled up in this order. The rubbing direction(RD) for aligning the discotic compound is essentially at the angle of45° to the slow axis (SA) of the second optically anisotropic layer(133), and the slow axis (SA) of the second optically anisotropic layer(133) is essentially parallel to the transmission axis (TA) of thepolarizing membrane (134).

[0446] The embodiment of FIG. 9(b 2) also comprises a second opticallyanisotropic layer (133), a first optically anisotropic layer (131) and apolarizing membrane (134), piled up in this order. The rubbing direction(RD) for aligning the discotic compound is essentially at the angle of45° to the slow axis (SA) of the second optically anisotropic layer(133), and the slow axis (SA) of the second optically anisotropic layer(133) is essentially perpendicular to the transmission axis (TA) of thepolarizing membrane (134).

[0447] The embodiment of FIG. 9(b 3) has a second optically anisotropiclayer consisting of two sub-layers (133 a, 133 b). In that embodiment,at least one anisotropic sub-layer 2 (133 b, in FIG. 9b 3) is placed atthe position satisfying the aforementioned condition with the firstoptically anisotropic layer (131) and the polarizing membrane (134).Namely, the rubbing direction (RD) for aligning the discotic compound isessentially at the angle of 45° to the slow axis (SA2) of the aboveoptically anisotropic sub-layer 2 (133 b), and that slow axis (SA2) isessentially parallel to the transmission axis (TA) of the polarizingmembrane (134). The other anisotropic sub-layer 2 (133 a) is, as aconventional one, placed so that the slow axis (SA1) may be essentiallyparallel to the rubbing direction (RD).

[0448] The embodiment of FIG. 9(b 4) has a second optically anisotropiclayer consisting of two sub-layers (133 a, 133 b) each of which isplaced at the positions satisfying the aforementioned condition with thefirst optically anisotropic layer (131) and the polarizing membrane(134). Namely, the rubbing direction (RD) for aligning the discoticcompound is essentially at the angle of 45° to each of the slow axes(SA1, SA2) of the optically anisotropic sub-layers 2 (133 a, 133 b), andeach of the slow axes (SA1, SA2) is essentially parallel to thetransmission axis (TA) of the polarizing membrane (134).

[0449] The embodiment of FIG. 9(b 5) also has a second opticallyanisotropic layer consisting of two sub-layers (133 a, 133 b) both ofwhich are placed at the positions where they totally satisfy theaforementioned condition with the first optically anisotropic layer(131) and the polarizing membrane (134). Namely, the rubbing direction(RD) for aligning the discotic compound is essentially at the angle of45° to each of the slow axes (SA1, SA2) of the optically anisotropicsub-layers 2 (133 a, 133 b). The slow axis (SA1) of the opticallyanisotropic sub-layer 2 (133 a) far-off from both of the first opticallyanisotropic layer (131) and the polarizing membrane (134) is essentiallyperpendicular to the transmission axis (TA) of the polarizing membrane(134). The slow axis (SA2) of the optically anisotropic sub-layer 2 (133b) near both of the first optically anisotropic layer (131) and thepolarizing membrane (134) is essentially parallel to the transmissionaxis (TA) of the polarizing membrane (134).

[0450] The elliptically polarizing plate comprises a first opticallyanisotropic layer containing discotic molecules oriented in hybridalignment, another second optically anisotropic layer having theoptically anisotropic cellulose acetate film, and a polarizing membrane.

[0451] If the liquid crystal cell of OCB mode is used, the firstoptically anisotropic layer containing discotic compound preferably hasno optical axis giving the retardation value of 0. Further, thedirection giving the minimum absolute retardation value of the firstoptically anisotropic layer is preferably neither in the layer plane noralong the normal of the layer plane.

[0452] As the optical characters of the optically anisotropic layers 1and 2, the Re retardation value defined by the following formula (9) andthe Rth retardation value defined by the following formula (10a) or(10b) should be noticed.

Re=(nx−ny)×d  (9)

Rth[{(n2+n3)/2}−n1]×d  (10a)

Rth=[{(nx+ny)/2}−nz]×d  (10b)

[0453] In the formulas, nx is a refractive index in the plane along theslow axis of the first or second optically anisotropic layer; ny is arefractive index in the plane along the traveling axis of the first andsecond optically anisotropic layer; n1 is the minimum principal value ofrefractive index of the first optically anisotropic layer; n2 and n3 areother principal values of refractive index of the first opticallyanisotropic layer; nz is a refractive index along the thicknessdirection of the second optically anisotropic layer; and d is athickness of the first or second optically anisotropic layer.

[0454] The Re retardation value of the first optically anisotropic layermeasured at 550 nm (Re550) is preferably in the range of 10 to 100 nm.The Rth retardation value of the first optically anisotropic layermeasured at 550 nm (Rth550) is preferably in the range of 40 to 200 nm.The angle (β) between the normal of the film and the direction givingthe minimum principal value of refractive index of the first opticallyanisotropic layer is preferably in the range of 20 to 50°.

[0455] The Rth retardation value of the second optically anisotropiclayer measured at 550 nm (Rth550) is preferably in the range of 150 to300 nm, more preferably in the range of 180 to 280 nm. A preferred Reretardation value of the second-optically anisotropic layer measured at550 nm (Re550) depends upon the arrangement of the layer and thetransmission axis of the polarizing membrane. If the slow axis in theplane of the second optically anisotropic layer is essentiallyperpendicular to the transmission axis, the Re550 of the secondoptically anisotropic layer is preferably in the range of 1 to 20 nm,more preferably in the range of 1 to 15 nm. If the slow axis of thesecond optically anisotropic layer is essentially parallel to thetransmission axis, the Re550 is preferably in the range of 20 to 100 nm,more preferably in the range of 30 to 60 nm.

[0456] In the case where the plate has a second optically anisotropiclayer consisting of two sub-layers, two cellulose acetate films may beused. Otherwise, liquid crystal molecules may be aligned on a celluloseacetate film.

[0457] The liquid crystal display of the invention has an opticalcompensatory function with small wavelength dependence. The term “smallwavelength dependence” means that the difference between the Reretardation value of liquid crystal cell and the total Re retardationvalue of the two optically anisotropic layers 1 and 2 (total Reretardation value of all optically anisotropic layers 1 if twoelliptically polarizing plates are used) is not larger than 10 nm in thewavelength region of 400 to 700 nm. The elliptically polarizing plate inwhich the optically anisotropic layers 1 and 2 and the polarizingmembrane are arranged according to the invention can easily realize thatcondition.

[0458] In the first optically anisotropic layer, the molecules ofdiscotic compound are preferably aligned so that the angle between thedisc plane and the transparent support may be changed along thethickness (namely, the molecules are preferably oriented in hybridalignment). The optical axis of the discotic molecule is parallel to thenormal of the disc plane. The discotic compound has birefringence, andhence the refractive index in the disc plane is lager than that alongthe normal of the disc plane.

[0459] The first optically anisotropic layer is preferably formedthrough the steps of aligning the molecules of discotic compound withthe orientation layer described below, and fixing the aligned molecules.The aligned discotic molecules are preferably polymerized to fix.

[0460] There is no direction giving the retardation value 0 of the firstoptically anisotropic layer. In other words, the minimum retardationvalue of the first optically anisotropic layer is more than 0.

[0461] The orientation layer has a function of giving an orientationdirection of the discotic molecules in the first optically anisotropiclayer. Preferred examples of the orientation layer include a layer of anorganic compound (preferably polymer) subjected to rubbing treatment, anobliquely deposited layer of an inorganic compound, and a layer havingmicro grooves. Further, a built-up film formed according toLangmuir-Blodgett technique (LB technique) from ω-tricosanoic acid,dioctadecyldimethylammoniumchloride or methyl stearate can be used asthe orientation layer. In addition, a layer prepared by orientingdielectric materials by application of electric field or magnetic fieldcan be employed as the orientation layer.

[0462] The orientation layer is preferably made of a polymer subjectedto rubbing treatment. As the polymer, polyvinyl alcohol is preferred.Particularly, denatured polyvinyl alcohol having hydrophobic groups ispreferred. Since hydrophobic group has affinity with the discoticcompound in the first optically anisotropic layer, the discotic compoundcan be uniformly aligned with the hydrophobic groups introduced intopolyvinyl alcohol. The hydrophobic group is attached to the side chainor the end of the main chain of polyvinyl alcohol.

[0463] The hydrophobic group preferably is an aliphatic group (morepreferably an alkyl group or an alkenyl group) having 6 or more carbonatoms or an aromatic group.

[0464] In the case where the hydrophobic group is attached to the end ofthe main chain, a linking group is preferably introduced between thehydrophobic group and the end of the main chain. Examples of the linkinggroup include —S—, —C(CN)R¹—, —NR²—, —CS— and combinations thereof. Eachof R¹ and R² is hydrogen or an alkyl group having 1 to 6 carbon atoms(preferably is an alkyl group having 1 to 6 carbon atoms).

[0465] In the case where the hydrophobic group is attached to the sidechain, the acetyl group (—CO—CH₃) of the vinyl acetate units inpolyvinyl alcohol is partially replaced with an acyl group (—CO—R³)having 7 or more carbon atoms. R³ is an aliphatic group having 6 or morecarbon atoms or an aromatic group. Commercially available denaturedpolyvinyl alcohols (e.g., MP103, MP203, R1130, Kuraray Co., Ltd.) can beused.

[0466] The (denatured) polyvinyl alcohol has a saponification degreepreferably of 80% or more. The (denatured) polyvinyl alcohol has apolymerization degree preferably of 200 or more.

[0467] The rubbing treatment can be conducted by rubbing the layer withpaper or cloth several times along a certain direction. Cloth on whichfibers having the same length and thickness are provided is preferablyused.

[0468] After the discotic molecules in the first optically anisotropiclayer are aligned with the orientation layer, they can keep thealignment even if the orientation layer is removed. Therefore, theorientation layer is not essential in a prepared elliptically polarizingplate though it is essential in the preparation of the plate.

[0469] In the case where the orientation layer is provided between theoptically anisotropic layers 1 and 2, an under-coating layer (anadhesive layer) is preferably provided between the orientation layer andthe second optically anisotropic layer.

[0470] The second optically anisotropic layer comprises at least onecellulose acetate film. The thickness of the cellulose acetate film ispreferably in the range of 10 to 70 μm. In the invention, the aimedoptical characters are preferably realized with a single celluloseacetate film, two cellulose acetate films or a layered composition ofcellulose acetate film and polymerizable liquid crystal compound. If thesecond optically anisotropic layer comprises two sub-layers (forexample, two cellulose acetate films), an intermediate layer (e.g.,adhesive layer) may be provided between them. In the second opticallyanisotropic layer consisting of two or more sub-layers, the sub-layerscooperatively realize the aimed optical characters.

[0471] The Re retardation value of the cellulose acetate film can beincreased by stretching the film. On the other hand, the Rth retardationvalue can be increased by (1) adding a retardation increasing agent, (2)adjusting the average acetic acid content of the cellulose acetate, and(3) forming the film according to the cooling dissolution method.

[0472] The cellulose acetate film may be used as a support, and apolymerizable liquid crystal layer containing horizontally alignedliquid crystal molecules may be provided thereon.

[0473] As the polymerizable liquid crystal compound, rod-like ordiscotic liquid crystal compounds are preferred. In consideration ofcontrolling the Rth retardation value, a discotic liquid crystalcompound is preferred.

[0474] The elliptically polarizing plate can be continuously produced inthe following manner.

[0475] First, an orientation layer is formed on a cellulose acetate film(second optically anisotropic layer) before-hand controlled to havedesired Re and Rth retardation values. While the film is being conveyedin the direction parallel to the slow axis, the formed orientation layeris then rubbed (rubbing treatment) at the angle of 45° to the conveyingdirection (which correspond to the slow axis). Nest, a layer of discoticcompound (first optically anisotropic layer) is formed on theorientation layer, and then the film is wound up. The cellulose acetatesurface of the film is saponified, and laminated on a polarizingmembrane with an adhesive. (On the other surface of the film, asaponified commercially available triacetyl cellulose film is laminatedwith an adhesive.)

[0476] In the case where the second optically anisotropic layercomprises two cellulose acetate films, the discotic compound is appliedon one cellulose acetate film to form a first optically anisotropiclayer in the above manner. A thin film is then laminated on the firstoptically anisotropic layer to protect the layer from scratching anddust, and then the layered film is wound up.

[0477] Independently, the other cellulose acetate film is saponified,and laminated on a polarizing membrane with an adhesive. (On the othersurface of the film, a saponified commercially available triacetylcellulose film is laminated with an adhesive.)

[0478] The layered film having the polarizing membrane and the woundedlayered film having the thin film are then laminated so that thecellulose acetate surface of each layered film may be in contact.

[0479] In the case where the second optically anisotropic layercomprises a cellulose acetate film and a polymerizable liquid crystal,the discotic compound is applied on a cellulose acetate film to form afirst optically anisotropic layer in the above manner. A thin film isthen laminated on the first optically anisotropic layer to protect thelayer from scratching and dust, and then the layered film is wound up.

[0480] Independently, an orientation film made of cellulose acetate isprepared. A layer containing horizontally aligned discotic molecules isformed on the orientation film, and the film is then saponified. Thefilm is laminated on a polarizing membrane with an adhesive. (On theother surface of the film, a saponified commercially available triacetylcellulose film is laminated with an adhesive.)

[0481] The film having the polarizing membrane and the wounded layeredfilm having the thin film are then laminated so that the celluloseacetate surface of each layered film may be in contact.

[0482] The elliptically polarizing plate of the invention isadvantageously combined with a liquid crystal cell of bend alignmentmode or horizontal alignment mode, to prepare a liquid crystal display.

[0483] In the liquid crystal cell of bend alignment mode, liquid crystalmolecules in the central area of the cell may be oriented in twistedalignment.

[0484] For ensuring both brightness and a wide viewing angle, the liquidcrystal cell of bend alignment mode has a product (Δn·d) of refractiveanisotropy (Δn) and thickness (d) of the cell preferably in the range of100 to 2,000 nm, more preferably in the range of 150 to 17,000 nm, mostpreferably in the range of 500 to 15,000 nm.

[0485] The liquid crystal cell of bend alignment mode can work accordingto normally white (NW) mode or normally black (NB) mode.

EXAMPLE 1

[0486] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0487] In another mixing tank, 16 weight parts of the followingretardation increasing agent, 80 weight parts of methylene chloride and20 weight parts of methanol were placed, heated and stirred, to preparea retardation increasing agent solution.

[0488] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 5.5 weight parts based on100 weight parts of cellulose acetate.

[0489] (Retardation Increasing Agent)

[0490] The dope was cast on a band to form a film in which the solventremained in the amount of 15 wt. %. The film was laterally stretched by25% at 130° C. by means of a tenter. Thus, a cellulose acetate film(optical compensatory sheet: KH-01) was prepared.

[0491] The Re and Rth retardation values of the prepared celluloseacetate film were measured at 550 nm by means of an ellipsometer [M-150,JASCO], to obtain the values of Re550 and Rth550. The results are setforth in Table 1.

[0492] The thickness of the prepared film was measured at 100 points inan area of 1 m×1 m by means of a digital film thickness gauge (K-402B,Anristu Co., Ltd.), and thereby it was found that the average thicknesswas 52.0 μm and that the standard deviation was 1.5 μm.

EXAMPLE 2

[0493] The procedure of Example 1 was repeated except that 474 weightparts of the cellulose acetate solution and 56 weight parts of theretardation increasing agent solution were mixed (7.8 weight parts ofthe retardation increasing agent was used based on 100 weight parts ofcellulose acetate) to prepare a dope, and except that the formed filmwas laterally stretched by 12%. Thus, a cellulose acetate film (opticalcompensatory sheet: KH-02) was prepared and evaluated. The results areset forth in Table 1.

[0494] The obtained film was immersed in a 1.5 N aqueous KOH solutionfor 5 minutes (40° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-treated film wasmeasured according to the contact angle method, to find 68 mN/m.

[0495] The thickness of the prepared film was measured at 100 points inan area of 1 m×1 m by means of a digital film thickness gauge (K-402B,Anristu Co., Ltd.), and thereby it was found that the average thicknesswas 40.0 μm and that the standard deviation was 1.8 μm.

[0496] On the cellulose acetate film, a coating solution of thefollowing composition was then applied in the amount of 28 ml/m² bymeans of a wire bar coater of #16. The applied solution was dried withhot air at 60° C. for 60 seconds, and then further dried with hot air at90° C. for 150 seconds. Coating solution for orientation film Thefollowing denatured polyvinyl alcohol 10 weight parts Water 371 weightparts Methanol 119 weight parts Glutaric aldehyde (crosslinking agent)0.5 weight part (Denatured polyvinyl alcohol)

[0497] The formed orientation layer was subjected to the rubbingtreatment in which the rubbing direction was at the angle of 45° to theslow axis (measured at 632.8 nm) of the cellulose acetate film.

[0498] (Formation of Optically Anisotropic Layer)

[0499] To prepare a coating solution, 41.01 g of the following discotic(liquid crystal) compound, 4.06 g of trimethylolpropane triacrylatedenatured with ethylene oxide (V#360, Osaka Organic Chemicals Co.,Ltd.), 0.90 g of cellulose acetate butyrate (CAB-551-0.2, EastmanChemical), 0.23 g of cellulose acetate butyrate (CAB-531-1, EastmanChemical), 1.35 g of a photopolymerization initiator (Irgacure 907,Ciba-Geigy) and 0.45 g of a sensitizer (Kayacure DETX, Nippon KayakuCo., Ltd.) were dissolved in 102 g of methyl ethyl ketone. The coatingsolution was then applied on the orientation film by means of a wire barcoater of #3. The thus-treated film was fixed on a metal frame, andmaintained in a thermostat at 130° C. for 2 minutes to align themolecules of the discotic compound. The film was then irradiated at 130°C. for 1 minute with ultraviolet rays emitted from a high pressuremercury lamp of 120 W/cm, to polymerize the discotic compound. The filmwas cooled to room temperature. Thus, an optical compensatory sheet(KH-12) having an optically anisotropic layer was formed.

[0500] The Re retardation value was measured at 550 nm, and found 38 nm.The average angle (inclined angle) between the disc plane and thecellulose acetate film was 40°.

[0501] (Discotic Liquid Crystal Compound)

EXAMPLE 3

[0502] The procedure of Example 1 was repeated except that 6.0 weightparts of the retardation increasing agent was used based on 100 weightparts of cellulose acetate to prepare a dope, and except that the formedfilm was laterally stretched by 30%. Thus, a cellulose acetate film(optical compensatory sheet: KH-03) was prepared and evaluated. Theresults are set forth in Table 1.

[0503] The obtained film was immersed in a 2.0 N aqueous KOH solutionfor 2 minutes (25° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-treated film wasmeasured according to the contact angle method, to find 63 mN/m.

[0504] The thickness of the prepared film was measured at 100 points inan area of 1 m×1 m by means of a digital film thickness gauge (K-402B,Anristu Co., Ltd.), and thereby it was found that the average thicknesswas 38.5 μm and that the standard deviation was 1.4 μm.

COMPARATIVE EXAMPLE 1

[0505] The procedure of Example 1 was repeated except that the celluloseacetate solution was directly used as a dope and that the film was notstretched, to form and evaluate a cellulose acetate film (opticalcompensatory sheet: KH-H1). The results are set forth in Table 1.

[0506] The thickness of the prepared film was measured at 100 points inan area of 1 m×1 m by means of a digital film thickness gauge (K-402B,Anristu Co., Ltd.), and thereby it was found that the average thicknesswas 80.5 μm and that the standard deviation was 1.7 μm. TABLE 1Retardation in- Stretching Film creasing agent ratio Re550 Rth550Example 1 KH-01 5.5 weight parts 25% 40 nm 130 nm Example 2 KH-02 7.8weight parts 12% 20 nm 110 nm Example 3 KH-03 6.0 weight parts 30% 50 nm130 nm Comp. Ex. 1 KH-H1 — —  4 nm  48 nm

EXAMPLE 4

[0507] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-01)prepared in Example 1 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive.

[0508] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive.

[0509] The transmission axis of the polarizing membrane was placedparallel to the slow axis of the optical compensatory sheet (KH-01)prepared in Example 1, and perpendicular to the slow axis of thecommercially available cellulose triacetate film. Thus, a polarizingplate was prepared.

EXAMPLE 5

[0510] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-O₂)prepared in Example 2 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that the slowaxis of the sheet might be parallel to the transmission axis of themembrane.

[0511] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive.

[0512] Further, the optical compensatory sheet (KH-12) prepared inExample 2 was laminated on the KH-02 side with an adhesive so that theslow axis of KH-12 might be parallel to that of KH-O₂. Thus, apolarizing plate was prepared.

EXAMPLE 6

[0513] The procedure of Example 4 was repeated except that the opticalcompensatory sheet (KH-03) prepared in Example 3 was used, to prepare apolarizing plate.

EXAMPLE 7

[0514] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Example 4 was laminated on theobserver side of the cell with an adhesive so that the KH-01 (opticalcompensatory sheet prepared in Example 1) might be on the liquid crystalcell side. On the other side (backlight side) of the cell, acommercially available polarizing plate (HLC2-5618HCS, Sunritz Co.,Ltd.) was laminated. The polarizing plate on the observer side wasplaced so that the transmission axis might be in the up-down direction,while the plate on the backlight side was placed so that thetransmission axis might be in the left-right direction. Thus, thepolarizing plates were arranged in cross-Nicol position.

[0515] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 2.

COMPARATIVE EXAMPLE 2

[0516] The viewing angle of the commercially available liquid crystaldisplay (VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cellcomprising vertically aligned liquid crystal molecules, was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 2. TABLE 2 Liquid Viewing angle* crystal along thetransmis- at 45° to the transmis- display sion axis sion axis Example7 >80° >80° Comp. Ex. 2 >80°   44°

[0517] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0518] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of 15 inches type (VL-1530S, Fujitsu,Ltd.), which has a liquid crystal cell comprising vertically alignedliquid crystal molecules. In place of the removed members, thepolarizing plate prepared in Example 4 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet might be on the liquidcrystal cell side. The polarizing plates were placed so that thetransmission axis of the plate on the observer side might beperpendicular to that on the backlight side.

[0519] The backlight of the prepared display had been kept on for 5hours under the conditions of 25° C. and 60% RH. After that, while ablack image was displayed on the whole screen, it was observed with theeyes in a dark room whether light leaked or not. As a result, it wasconfirmed that the display of 15 inches type equipped with thepolarizing plate of Example 4 did not leak light at the peripheral partof the screen.

EXAMPLE 8

[0520] (Preparation of Liquid Crystal Cell of Bend Alignment Mode)

[0521] On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having An of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment.

[0522] Two elliptically polarizing plates prepared in Example 5 werelaminated on the liquid crystal cell so that the cell might be betweenthe plates. The plates were arranged so that the optically anisotropiclayer in each plate might face to the cell substrate and that therubbing directions of the cell and the optically anisotropic layer mightbe ant-parallel.

[0523] Voltage of a square wave (55 Hz) was applied to the liquidcrystal cell. An image was displayed according to normally white mode(white: 2V, black: 5V). A ratio of the transmittance (white/black) wasmeasured as a contrast ratio by means of a meter (EZ-Contrast 160D,ELDIM) at eight displaying states of L1 (full black) to L8 (full white).From the obtained contrast ratio, the viewing angle of the preparedliquid crystal display was measured. The results are set forth in Table3. TABLE 3 Viewing angle* LCD Upward Downward Left-rightward Example 880° 80° 80°

[0524] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0525] A 17 inches type liquid crystal cell of bend alignment modeequipped with two polarizing plates of Example 5 was prepared in theabove manner.

[0526] A backlight was attached on the prepared cell, and had been kepton for 5 hours under the conditions of 25° C. and 60% RH. After that,while a black image was displayed on the whole screen, it was observedwith the eyes in a dark room whether light leaked or not. As a result,it was confirmed that the cell equipped with the polarizing plates ofExample 5 did not leak light at the peripheral part of the screen.

EXAMPLE 9

[0527] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 6 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the KH-03 (optical compensatory sheet prepared inExample 3) might be on the liquid crystal cell side. The polarizingplates were arranged so that the transmission axes might be in O-modeposition (be perpendicularly crossed).

[0528] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 4.

COMPARATIVE EXAMPLE 3

[0529] The viewing angle of the commercially available liquid crystaldisplay (6E-A3, Sharp Corporation), which has a liquid crystal cell ofTN mode, was measured by means of a measuring apparatus (EZ-Contrast160D, ELDIM) when each of eight tones of black (L1) to white (L8) wasdisplayed. The results are set forth in Table 4. TABLE 4 Viewing angle*LCD Upward Downward Left-rightward Example 9 18° 23° 77° Comp. Ex. 3 15°25° 37°

[0530] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0531] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of 20 inches type (LC-20V1, SharpCorporation), which had a liquid crystal cell of TN mode. In place ofthe removed members, the polarizing plate prepared in Example 6 waslaminated on each side (each of the backlight side and the observerside) of the cell with an adhesive so that the optical compensatorysheet might be on the liquid crystal cell side. The polarizing plateswere placed so that the transmission axis of the plate on the observerside might be perpendicular to that on the backlight side.

[0532] The backlight of the prepared display had been kept on for 5hours under the conditions of 25° C. and 60% RH. After that, while ablack image was displayed on the whole screen, it was observed with theeyes in a dark room whether light leaked or not. As a result, it wasconfirmed that the display of 20 inches type equipped with thepolarizing plate of Example 6 did not leak light at the peripheral partof the screen.

EXAMPLE 10

[0533] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0534] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0535] The cellulose acetate solution (468 weight parts) and theretardation increasing agent solution (32 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 4.5 weight parts based on100 weight parts of cellulose acetate.

[0536] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried for 1 minute. After peeled from the band, thefilm was uniaxially (laterally) stretched by 35% with a tenter whileexposed to drying air at 130° C. The film was then uniaxially(longitudinally) stretched by 10% in the conveying direction whileexposed to drying air at 140° C. The thus stretched film was furtherdried with air at 130° C. for about 15 minutes, to prepare a celluloseacetate film (thickness: 50 μm) in which the solvent remained in theamount of 0.3 wt. %.

[0537] The Re and Rth retardation values of the prepared celluloseacetate film (KH-04) were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to obtain the values of Re550 and Rth550. The resultsare set forth in Table 5.

EXAMPLE 11

[0538] The dope prepared in Example 10 was cast on a band by means of aband casting machine. When the temperature of the dope on the bandreached 40° C., the formed film was dried for 1 minute. After peeledfrom the band, the film was uniaxially (laterally) stretched by 20% witha tenter while exposed to drying air at 130° C. The film was thenuniaxially (longitudinally) stretched by 8% in the conveying directionwhile exposed to drying air at 140° C. The thus stretched film wasfurther dried with air at 130° C. for about 15 minutes, to prepare acellulose acetate film (thickness: 58 μm) in which the solvent remainedin the amount of 0.3 wt. %.

[0539] The Re and Rth retardation values of the prepared celluloseacetate film (KH-05) were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to obtain the values of Re550 and Rth550. The resultsare set forth in Table 5.

[0540] The obtained film was immersed in a 2.0 N aqueous KOH solutionfor 2 minutes (25° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-saponified film wasmeasured according to the contact angle method, to find 63 mN/m.

[0541] On the cellulose acetate film, the coating solution used inExample 2 was then applied in the amount of 28 ml/m² by means of a wirebar coater of #16. The applied solution was dried with hot air at 60° C.for 60 seconds, and then further dried with hot air at 90° C. for 150seconds.

[0542] The formed layer was subjected to the rubbing treatment in whichthe rubbing direction was at the angle of 450 to the longitudinaldirection of the cellulose acetate film.

[0543] (Formation of Optically Anisotropic Layer.)

[0544] To prepare a coating solution, 41.01 g of the discotic (liquidcrystal) compound used in Example 2, 4.06 g of trimethylolpropanetriacrylate denatured with ethylene oxide (v#360, Osaka OrganicChemicals Co., Ltd.), 0.90 g of cellulose acetate butyrate (CAB-551-0.2,Eastman Chemical), 0.23 g of cellulose acetate butyrate (CAB-531-1,Eastman Chemical), 1.35 g of a photopolymerization initiator (Irgacure907, Ciba-Geigy) and 0.45 g of a sensitizer (Kayacure DETX, NipponKayaku Co., Ltd.) were dissolved in 102 g of methyl ethyl ketone. Thecoating solution was then applied on the orientation layer by means of awire bar coater of #3.6. The thus-treated film was heated in athermostat-at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 60° C. for 1 minutewith ultraviolet rays emitted from a high pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optical compensatory sheet (KH-15) having anoptically anisotropic layer was formed.

[0545] The Re retardation value was measured at 550 nm, and found 43 nm.The average angle (inclined angle) between the disc plane and thecellulose acetate film was 42°.

EXAMPLE 12

[0546] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.7%) Polyesterurethane (B-326, Sumitomo 16 weight partsBayern Co., Ltd.; Desmocol 176) Methylene chloride (first solvent) 300weight parts Methanol (second solvent) 54 weight parts 1-Butanol (thirdsolvent) 11 weight parts

[0547] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0548] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (26 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0549] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried for 1 minute. After peeled from the band, thefilm was laterally stretched by 40% with a tenter while the solventremained in the amount of 15 wt. %. The film was then longitudinallystretched by 28% while exposed to drying air at 130° C. so that thesolvent might remain in the amount of 5 wt. %. The thus stretched filmwas further dried with air at 140° C., to prepare a cellulose acetatefilm (thickness: 40 μm) in which the solvent remained in the amount of0.3 wt. %.

[0550] The Re and Rth retardation values of the prepared celluloseacetate film (KH-06) were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to obtain the values of Re550 and Rth550. The resultsare set forth in Table 5.

[0551] The prepared film was saponified, and an orientation layer and anoptically anisotropic layer were provided thereon to produce an opticalcompensatory sheet (KH-16) in the same manner as Example 11.

EXAMPLE 13

[0552] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.7%) Methylene chloride (first solvent) 300 weight partsMethanol (second solvent) 54 weight parts 1-Butanol (third solvent) 11weight parts Boron nitride powder (highly 30 weight partsthermo-conductive particles)

[0553] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0554] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0555] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried for 1 minute. After peeled from the band, thefilm was uniaxially (laterally) stretched by 38% with a tenter whileexposed to drying air at 140° C. The thus stretched film was dried withair at 135° C. for about 20 minutes, to prepare a cellulose acetate film(thickness: 65 μm) in which the solvent remained in the amount of 0.3wt. %.

[0556] The thermal conductivity of the prepared cellulose acetate filmwas measured in the following manner, to find 1.2 W/(m·K).

[0557] The sample film is placed between a copper heater case and acopper plate in TO-3 type hater, and is pressed by 10%. The film is thenkept for 4 minutes while the copper heater case is electrified at 5 W,and the temperature difference between the case and the plate ismeasured. From the obtained date, the thermal conductivity is calculatedaccording to the formula:

Thermal conductivity {W/(m·K)}={electric power (W)×thickness(m)}/{temperature difference (K)×measured area (m²)}.

[0558] The Re and Rth retardation values of the prepared celluloseacetate film (KH-07) were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to obtain the values of Re550 and Rth550. The resultsare set forth in Table 5.

[0559] The obtained cellulose acetate film (KH-07) was immersed in a 1.5N aqueous KOH solution for 5 minutes (40° C.), neutralized with sulfuricacid, washed with pure water, and dried. The surface energy of thethus-saponified film was measured according to the contact angle method,to find 68 mN/m.

[0560] (Formation of Orientation Layer)

[0561] On the prepared cellulose acetate film, a coating solution fororientation layer used in Example 2 was applied by means of a wire-barcoater #16 in the amount of 28 ml/m². The applied solution was driedwith hot air at 60° C. for 60 seconds, and then further dried with hotair at 90° C. for 150 seconds.

[0562] The formed orientation layer was subjected to the rubbingtreatment in which the rubbing direction was at the angle of 450 to theslow axis (measured at 632.8 nm) of the cellulose acetate film.

[0563] (Preparation of Liquid Crystal Compound)

[0564] A liquid crystal polymer was synthesized, and it was confirmedthat the polymer was oriented in homeotropic alignment on a substratenot subjected to orienting treatment.

[0565] For synthesizing the polymer, 10 mmol of 4-n-heptyl benzoic acid,95 mmol of terephthalic acid, 50 mmol of methylhydroquinone diacetate,50 mmol of catechol diacetate and 100 mg of sodium acetate were used toperform polymerization at 270° C. for 12 hours under nitrogenatmosphere. The reaction product was dissolved in tetrachloroethane, andre-precipitated with methanol to obtain 22.0 g of liquid crystalpolyester. The prepared liquid crystal polyester had the logarithmicviscosity of 0.15, and formed a nematic phase as a liquid crystal phase.The phase transition temperature between the isotropic phase and theliquid crystal phase was observed at 240° C., and the glass transitionpoint was found at 75° C.

[0566] A 10 wt. % solution of the liquid crystal polyester dissolved ina mixed solvent of phenol/tetrachloroethane (6/4, by weight) wasprepared, and applied on a plate of soda glass according to the bar-coatmethod. After the solvent was removed, the applied polyester wassubjected to heat treatment at 190° C. for 30 minutes, and then left atroom temperature to cool and fix. As a result, an evenly oriented liquidcrystal film having the thickness of 15 μm was prepared. The film wasobserved through a conoscope, and thereby it was found that the liquidcrystal polymer had positive uniaxiality to form homeotropic alignment.

[0567] (Formation of Optically Anisotropic Layer)

[0568] An 8 wt. % tetrachloroethane solution of the liquid crystalpolyester was prepared, and applied on the above orientation layeraccording to the spin-coat method. After the solvent was removed, theapplied polyester was subjected to heat treatment at 190° C. for 20minutes, and then left at room temperature to cool and fix. Thethus-formed optical compensatory sheet (KH-17) was transparent, and hadno aligning defect and an even thickness (1.55 μm).

COMPARATIVE EXAMPLE 4

[0569] The procedure of Example 10 was repeated except that thecellulose acetate solution was directly used as a dope and that the filmwas not stretched, to form and evaluatea cellulose acetate film (opticalcompensatory sheet: KH-H2) containing the remaining solvent in theamount of 3.0 wt. % and the thickness of 80 μm. The results are setforth in Table 5. TABLE 5 Retardation in- Film creasing agent Re550Rth550 Example 10 KH-04 4.5 weight parts 45 nm 135 nm Example 11 KH-054.5 weight parts 35 nm 125 nm Example 12 KH-06 3.5 weight parts 25 nm120 nm Example 13 KH-07 3.5 weight parts 50 nm  90 nm Comp. Ex. 4 KH-H2—  4 nm  48 nm

EXAMPLE 14

[0570] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-04)prepared in Example 10 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive.

[0571] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive.

[0572] The transmission axis of the polarizing membrane was placedparallel to the slow axis of the optical compensatory sheet (KH-04).Thus, a polarizing plate was prepared.

EXAMPLE 15

[0573] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-15)prepared in Example 11 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (KH-05) (support of the compensatory sheet) mightbe on the polarizing membrane side and so that the slow axis of thesheet might be parallel to the transmission axis of the membrane.

[0574] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 16

[0575] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-16)prepared in Example 12 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (KH-06) (support of the compensatory sheet) mightbe on the polarizing membrane side and so that the slow axis of thesheet might be parallel to the transmission axis of the membrane.

[0576] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 17

[0577] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-17)prepared in Example 13 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (KH-07) (support of the compensatory sheet) mightbe on the polarizing membrane side and so that the slow axis of thesheet might be parallel to the transmission axis of the membrane.

[0578] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

COMPARATIVE EXAMPLE 5

[0579] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-H2)prepared in Comparative Example 4 was then laminated on one surface ofthe polarizing membrane with a polyvinyl alcohol adhesive.

[0580] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 18

[0581] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Example 14 was laminated onthe observer side of the cell with an adhesive so that the opticalcompensatory sheet (KH-04) might be on the liquid crystal cell side. Onthe other side (backlight side) of the cell, a commercially availablepolarizing plate (HLC2-5618HCS, Sunritz Co., Ltd.) was laminated. Thepolarizing plate on the observer side was placed so that thetransmission axis might be in the up-down direction, while the plate onthe backlight side was placed so that the transmission axis might be inthe left-right direction. Thus, the polarizing plates were arranged incross-Nicol position.

[0582] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 6.

COMPARATIVE EXAMPLE 6

[0583] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Comparative Example 5 waslaminated on the observer side of the cell with an adhesive so that theoptical compensatory sheet (KH-H2) might be on the liquid crystal cellside. On the other side (backlight side) of the cell, a commerciallyavailable polarizing plate (HLC2-5618HCS, Sunritz Co., Ltd.) waslaminated. The polarizing plate on the observer side was placed so thatthe transmission axis might be in the up-down direction, while the plateon the backlight side was placed so that the transmission axis might bein the left-right direction. Thus, the polarizing plates were arrangedin cross-Nicol position.

[0584] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 6. TABLE 6 Liquid Viewing angle* crystalalong transmission at 45° to the trans- display axis mission axisExample 18 >80° >80° Comp. Ex. 6 >80°   44°

[0585] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0586] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of 15 inches type (VL-1530S, Fujitsu,Ltd.), which has a liquid crystal cell comprising vertically alignedliquid crystal molecules. In place of the removed members, thepolarizing plate prepared in Example 14 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet might be on the liquidcrystal cell side. The polarizing plates were placed so that thetransmission axis of the plate on the observer side might beperpendicular to that on the backlight side. The polarizing plateprepared in Comparative Example 5 was also installed in the liquidcrystal display.

[0587] The backlight of the prepared display had been kept on for 5hours under the conditions of 25° C. and 60% RH. After that, while ablack image was displayed on the whole screen, it was observed with theeyes in a dark room whether light leaked or not. As a result, it wasconfirmed that the display of 15 inches type equipped with thepolarizing plate of Example 14 did not leak light at the peripheral partof the screen but that the display equipped with the plate ofComparative Example 5 leaked light.

EXAMPLE 19

[0588] (Preparation of Liquid Crystal Cell of Bend Alignment Mode)

[0589] On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having Δn of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment (17 inches type).

[0590] (Production of Liquid Crystal Display)

[0591] Two elliptically polarizing plates prepared in Example 15 werelaminated on the liquid crystal cell so that the cell might be betweenthe plates. The plates were arranged so that the optically anisotropiclayer in each plate might face to the cell substrate and that therubbing directions of the cell and the optically anisotropic layer mightbe anti-parallel.

[0592] Voltage of a square wave (55 Hz) was applied to the liquidcrystal cell. An image was displayed according to normally white mode(white: 2V, black: 5V). A ratio of the transmittance (white/black) wasmeasured as a contrast ratio by means of a meter (EZ-Contrast 160D,ELDIM) at eight displaying states of L1 (full black) to L8 (full white).From the obtained contrast ratio, the viewing angle of the preparedliquid crystal display was measured. The results are set forth in Table7.

EXAMPLE 20

[0593] (Preparation of Liquid Crystal Cell of Bend Alignment Mode)

[0594] On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having Δn of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment (17 inches type).

[0595] (Production of Liquid Crystal Display)

[0596] Two elliptically polarizing plates prepared in Example 16 werelaminated on the liquid crystal cell so that the cell might be betweenthe plates. The plates were arranged so that the optically anisotropiclayer in each plate might face to the cell substrate and that therubbing directions of the cell and the optically anisotropic layer mightbe anti-parallel.

[0597] Voltage of a square wave (55 Hz) was applied to the liquidcrystal cell. An image was displayed according to normally white mode(white: 2V, black: 5V). A ratio of the transmittance (white/black) wasmeasured as a contrast ratio by means of a meter (EZ-Contrast 160D,ELDIM) at eight displaying states of L1 (full black) to L8 (full white).From the obtained contrast ratio, the viewing angle of the preparedliquid crystal display was measured. The results are set forth in Table7. TABLE 7 Viewing angle* LCD Upward Downward Left-rightward Example 1980° 80° 80° Example 20 80° 80° 80°

[0598] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0599] A backlight was attached on the cell prepared in each of Examples19 and 20, and had been kept on for 5 hours under the conditions of 25°C. and 60% RH. After that, while a black image was displayed on thewhole screen, it was observed with the eyes in a dark room whether lightleaked or not. As a result, it was confirmed that the cell equipped withthe polarizing plates prepared in each of Examples 19 and 20 did notleak light at the peripheral part of the screen.

EXAMPLE 21

[0600] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 17 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the KH-07 (optical compensatory sheet prepared inExample 17) might be on the liquid crystal cell side. The polarizingplates were arranged so that the transmission axes might be crossedperpendicularly.

[0601] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 8. TABLE 8 Viewing angle* LCD UpwardDownward Left-rightward Example 21 35° 60° 80°

[0602] (Evaluation of Increase of Transmittance at the Peripheral Partof the Screen)

[0603] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of 20 inches type (LC-20VI, SharpCorporation), which had a liquid crystal cell of TN mode. In place ofthe removed members, the polarizing plate prepared in Example 17 waslaminated on each side (each of the backlight side and the observerside) of the cell with an adhesive so that the optical compensatorysheet might be on the liquid crystal cell side. The polarizing plateswere placed so that the transmission axis of the plate on the observerside might be perpendicular to that on the backlight side.

[0604] The backlight of the prepared display had been kept on for 5hours under the conditions of 25° C. and 60% RH. After that, while ablack image was displayed on the whole screen, it was observed with theeyes in a dark room whether light leaked or not. As a result, it wasconfirmed that the display of 20 inches type equipped with thepolarizing plate of Example 17 did not leak light at the peripheral partof the screen.

EXAMPLE 22

[0605] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0606] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0607] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0608] The prepared dope was cast on a band by means of a band castingmachine. After peeled from the band, the film was laterally stretched by25% at 130° C. with a tenter while the solvent remained in the amount of15 wt. %, to prepare a cellulose acetate film (thickness: 70 μm).

[0609] The obtained film was immersed in a 1.5 N aqueous KOH solutionfor 2 minutes (50° C.), and neutralized with sulfuric acid. After takenout of the solution, the film was washed with pure water, and dried. Thesurface energy of the thus-saponified film was measured according to thecontact angle method, to find 60 mN/m.

[0610] The Re and Rth retardation values of the prepared celluloseacetate film (optical compensatory sheet) were measured at 550 nm bymeans of an ellipsometer [M-150, JASCO], to obtain the values of Re550and Rth550. The results are set forth in Table 9.

EXAMPLE 23

[0611] The procedure of Example 22 was repeated except that 474 weightparts of the cellulose acetate solution and 56 weight parts of theretardation increasing agent solution were mixed (7.8 weight parts ofthe retardation increasing agent was used based on 100 weight parts ofcellulose acetate) to prepare a dope, and except that the formed filmwas stretched by 14%. Thus, a cellulose acetate film (opticalcompensatory sheet) was prepared.

[0612] The obtained film was immersed in a 1.5 N aqueous KOH solutionfor 5 minutes (40° C.), and neutralized with sulfuric acid. After takenout of the solution, the film was washed with pure water, and dried. Thesurface energy of the thus-saponified film was measured according to thecontact angle method, to find 68 mN/m.

[0613] The Re and Rth retardation values of the prepared celluloseacetate film (optical compensatory sheet) were measured at 550 nm bymeans of an ellipsometer [M-150, JASCO], to obtain the values of Re550and Rth550. The results are set forth in Table 9.

EXAMPLE 24

[0614] The procedure of Example 23 was repeated except that the formedfilm was stretched by 8%, to prepare a cellulose acetate film.

[0615] The obtained film was immersed in a 2.0 N aqueous KOH solutionfor 2 minutes (25° C.), and neutralized with sulfuric acid. After takenout of the solution, the film was washed with pure water, and dried. Thesurface energy of the thus-saponified film was measured according to thecontact angle method, to find 63 mN/m.

[0616] On the prepared cellulose acetate film, a coating solution fororientation layer used in Example 2 was applied by means of a wire-barcoater #16 in the amount of 28 ml/m². The applied solution was driedwith hot air at 60° C. for 60 seconds, and then further dried with hotair at 90° C. for 150 seconds.

[0617] The formed layer was subjected to the rubbing treatment in whichthe rubbing direction was at the angle of 450° to the slow axis(measured at 632.8 nm) of the cellulose acetate film.

[0618] (Formation of Optically Anisotropic Layer)

[0619] To prepare a coating solution, 41.01 g of the discotic (liquidcrystal) compound used in Example 2, 4.06 g of trimethylolpropanetriacrylate denatured with ethylene oxide (V#360, Osaka OrganicChemicals Co., Ltd.), 0.90 g of cellulose acetate butyrate (CAB-551-0.2,Eastman Chemical), 0.23 g of cellulose acetate butyrate (CAB-531-1,Eastman Chemical), 1.35 g of a photopolymerization initiator (Irgacure907, Ciba-Geigy) and 0.45 g of a sensitizer (Kayacure DETX, NipponKayaku Co., Ltd.) were dissolved in 102 g of methyl ethyl ketone. Thecoating solution was then applied on the orientation film by means of awire bar coater of #3. The thus-treated film was fixed on a metal frame,and heated in a thermostat at 130° C. for 2 minutes to align themolecules of the discotic compound. The film was then irradiated at 130°C. for 1 minute with ultraviolet rays emitted from a high pressuremercury lamp of 120 W/cm, to polymerize the discotic compound. The filmwas cooled to room temperature. Thus, an optically anisotropic layer wasformed.

[0620] The Re and Rth retardation values (Re550 and Rth550) of theprepared optical compensatory sheet were measured at 550 nm in the samemanner as in Example 22. The results are set forth in Table 9.

EXAMPLE 25

[0621] The procedure of Example 22 was repeated except that 474 weightparts of the cellulose acetate solution and 56 weight parts of theretardation increasing agent solution were mixed (7.8 weight parts ofthe retardation increasing agent was used based on 100 weight parts ofcellulose acetate) to prepare a dope, and except that the formed filmwas stretched by 35%. Thus, a cellulose acetate film (opticalcompensatory sheet) was prepared.

[0622] The surface of the obtained film was subjected to coronadischarge treatment at the discharge frequency of 100 kHz, and then itssurface energy film was measured according to the contact angle methodto find 60 mN/m.

[0623] The Re and Rth retardation values (Re550 and Rth550) of theprepared cellulose acetate film (optical compensatory sheet) weremeasured at 550 nm in the same manner as in Example 22. The results areset forth in Table 9.

COMPARATIVE EXAMPLE 7

[0624] The procedure of Example 22 was repeated except that thecellulose acetate solution was directly used as a dope and that the filmwas not stretched, to form and evaluate a cellulose acetate film(optical compensatory sheet). The results are set forth in Table 9.TABLE 9 Retardation in- Stretching creasing agent ratio Re550 Rth550Example 22 3.5 weight parts 25% 40 nm 130 nm Example 23 7.8 weight parts14% 50 nm 240 nm Example 24 7.8 weight parts  8% 20 nm 220 nm Example 257.8 weight parts 35% 120 nm  250 nm Comp. Ex. 7 — —  4 nm  48 nm

EXAMPLE 26

[0625] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The cellulose acetate film prepared inExample 22 was then laminated on one surface of the polarizing membranewith a polyvinyl alcohol adhesive.

[0626] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive.

[0627] The transmission axis of the polarizing membrane was placedparallel to the slow axis of the film prepared in Example 22. Thetransmission axis of the polarizing membrane was placed perpendicularlyto the slow axis of the commercially available cellulose triacetatefilm. Thus, a polarizing plate was prepared.

EXAMPLE 27

[0628] The procedure of Example 26 was repeated except that thecellulose acetate film prepared in Example 23 was used, to prepare apolarizing plate.

EXAMPLE 28

[0629] The procedure of Example 26 was repeated except that thecellulose acetate film prepared in Example 24 was used, to prepare apolarizing plate.

EXAMPLE 29

[0630] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Example 26 was laminated oneach side (each of the backlight side and the observer side) of the cellwith an adhesive so that the cellulose acetate film prepared in Example22 might be on the liquid crystal cell side. The polarizing plate on theobserver side was placed so that the transmission axis might be in theup-down direction, while the plate on the backlight side was placed sothat the transmission axis might be in the left-right direction. Thus,the polarizing plates were arranged in cross-Nicol position.

[0631] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (LI) to white (L8) was displayed. Theresults are set forth in Table 10.

EXAMPLE 30

[0632] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Example 27 was laminated onthe observer side of the cell with an adhesive so that the celluloseacetate film prepared in Example 23 might be on the liquid crystal cellside. On the other side (backlight side) of the cell, a commerciallyavailable polarizing plate (HLC2-5618HCS, Sunritz Co., Ltd.) waslaminated. The polarizing plate on the observer side was placed so thatthe transmission axis might be in the up-down direction, while the plateon the backlight side was placed so that the transmission axis might bein the left-right direction. Thus, the polarizing plates were arrangedin cross-Nicol position.

[0633] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 10.

COMPARATIVE EXAMPLE 8

[0634] The viewing angle of the commercially available liquid crystaldisplay (VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cellcomprising vertically aligned liquid crystal molecules, was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 10. TABLE 10 Liquid Viewing angle* crystal alongtransmission at 45° to the transmis- display axis sion axis Example 2980° 80° Example 30 80° 80° Comp. Ex. 8 80° 44°

EXAMPLE 31

[0635] (Preparation of Liquid Crystal Cell of Bend Alignment Mode)

[0636] On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having Δn of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment.

[0637] Two elliptically polarizing plates prepared in Example 28 werelaminated on the liquid crystal cell so that the cell might be betweenthe plates. The plates were arranged so that the optically anisotropiclayer in each plate might face to the cell substrate and that therubbing directions of the cell and the optically anisotropic layer mightbe anti-parallel.

[0638] Voltage of a square wave (55 Hz) was applied to the liquidcrystal cell. An image was displayed according to normally white mode(white: 2V, black: 5V). A ratio of the transmittance (white/black) wasmeasured as a contrast ratio by means of a meter (EZ-Contrast 160D,ELDIM) at eight displaying states of L1 (full black) to L8 (full white).From the obtained contrast ratio, the viewing angle of the preparedliquid crystal display was measured. The results are set forth in Table11. TABLE 11 Viewing angle* LCD Upward Downward Left-rightward Example31 80° 80° 80°

EXAMPLE 32

[0639] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 26 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the cellulose acetate film prepared in Example 22 mightbe on the liquid crystal cell side. The polarizing plates were arrangedso that the transmission axes might be crossed perpendicularly.

[0640] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 12.

COMPARATIVE EXAMPLE 9

[0641] The viewing angle of the commercially available liquid crystaldisplay (6E-A3, Sharp Corporation), which has a liquid crystal cell ofTN mode, was measured by means of a measuring apparatus (EZ-Contrast160D, ELDIM) when each of eight tones of black (L1) to white (L8) wasdisplayed. The results are set forth in Table 12. TABLE 12 Viewingangle* LCD Upward Downward Left-rightward Example 32 18° 23° 77° Comp.Ex. 9 15° 25° 37°

EXAMPLE 33

[0642] (Preparation of Cellulose Acetate Film)

[0643] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasiticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0644] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0645] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0646] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried with air at 70° C. for 1 minute. After peeledfrom the band, the film was dried with air at 140° C. for about 10minutes, to prepare a cellulose acetate film (thickness: 50 μm) in whichthe solvent remained in the amount of 0.3 wt. %.

[0647] The Re and Rth retardation values of the prepared celluloseacetate film (CAF-01) were measured at 550 nm by means of anellipsometer [M-150, JASCO], to obtain the values of Re550 and Rth550.The results are set forth in Table 13.

[0648] The obtained film was immersed in a 2.0 N aqueous KOH solutionfor 2 minutes (25° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-saponified film wasmeasured according to the contact angle method, to find 63 mNIm.

[0649] (Formation of Orientation Layer)

[0650] on the prepared cellulose acetate film, the coating solution usedin Example 2 was then applied in the amount of 28 ml/m² by means of awire bar coater of #16. The applied solution was dried with hot air at60° C. for 60 seconds, and then further dried with hot air at 90° C. for150 seconds.

[0651] The formed layer was subjected to the rubbing treatment in whichthe rubbing direction was parallel to the longitudinal direction of thecellulose acetate film.

[0652] (Formation of Optically Anisotropic Layer)

[0653] To prepare a coating solution, 41.01 g of the discotic (liquidcrystal) compound used in Example 2, 4.06 g of trimethylolpropanetriacrylate denatured with ethylene oxide (V#360, Osaka OrganicChemicals Co., Ltd.), 0.90 g of cellulose acetate butyrate (CAB-551-0.2,Eastman Chemical), 0.23 g of cellulose acetate butyrate (CAB-531-1,Eastman Chemical), 1.35 g of a photopolymerization initiator (Irgacure907, Ciba-Geigy) and 0.45 g of a sensitizer (Kayacure DETX, NipponKayaku Co., Ltd.) were dissolved in 102 g of methyl ethyl ketone. Thecoating solution was then applied on the orientation film by means of awire bar coater of #3.6. The thus-treated film was heated in athermostat at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 60° C. for 1 minutewith ultraviolet rays emitted from a high pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optical compensatory sheet (KH-A1) was formed.

[0654] The Re retardation value was measured at 550 nm, and found 43 nm.The average angle (inclined angle) between the disc plane and thecellulose acetate film was 42°.

EXAMPLE 34

[0655] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.7%) Polyesterurethane (B-326, Sumitomo 16 weight partsBayern Co., Ltd.; Desmocol 176) Methylene chloride (first solvent) 300weight parts Methanol (second solvent) 54 weight parts 1-Butanol (thirdsolvent) 11 weight parts

[0656] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0657] The cellulose acetate solution (484 weight parts) and theretardation increasing agent solution (15 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 2.0 weight parts based on100 weight parts of cellulose acetate.

[0658] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried with air at 65° C. for 1 minute. After peeledfrom the band, the film was laterally stretched by 20% with a tenterwhile the solvent remained in the amount of 15 wt. %. The film was driedwith air at 130° C. for 5 minutes so that the solvent might remain inthe amount of 5 wt. %. The film was then longitudinally stretched by18%, and further dried with air at 140° C. for 10 minutes to prepare acellulose acetate film (thickness: 40 μm) in which the solvent remainedin the amount of 0.3 wt. %.

[0659] The Re and Rth retardation values of the prepared celluloseacetate film (CAF-₀₂) were measured at 550 nm by means of anellipsometer [M-150, JASCO], to obtain the values of Re550 and Rth550.The results are set forth in Table 13.

[0660] The prepared film was subjected to the surface treatment in thesame manner as Example 33, and an orientation layer and an opticallyanisotropic layer were provided thereon to produce an opticalcompensatory sheet (KH-A2).

EXAMPLE 35

[0661] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.7%) Methylene chloride (first solvent) 300 weight partsMethanol (second solvent) 54 weight parts 1-Butanol (third solvent) 11weight parts Boron nitride powder (highly 30 weight partsthermo-conductive particles)

[0662] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0663] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0664] The prepared dope was cast on a band by means of a band castingmachine. When the temperature of the dope on the band reached 40° C.,the formed film was dried with air at 70° C. for 1 minute. After peeledfrom the band, the film was dried with air at 140° C. for 10 minutes, toprepare a cellulose acetate film (thickness: 50 μm) in which the solventremained in the amount of 0.3 wt. %.

[0665] The thermal conductivity of the prepared cellulose acetate filmwas measured, to find 1.2 W/(m-K).

[0666] The optical characters of the cellulose acetate film (CAF-03)were measured. The results are set forth in Table 13.

[0667] The obtained film (CAF-03) was immersed in a 1.5 N aqueous KOHsolution for 5 minutes (40° C.), neutralized with sulfuric acid, washedwith pure water, and dried. The surface energy of the thus-saponifiedfilm (CAF-03) was measured according to the contact angle method, tofind 68 mN/m.

[0668] (Formation of Orientation Layer)

[0669] On the prepared cellulose acetate film, the coating solution usedin Example 2 was then applied in the amount of 28 ml/m² by means of awire bar coater of #16. The applied solution was dried with hot air at60° C. for 60 seconds, and then further dried with hot air at 90° C. for150 seconds.

[0670] The formed layer was subjected to the rubbing treatment in whichthe rubbing direction was parallel to the longitudinal direction of thecellulose acetate film.

[0671] (Preparation of Liquid Crystal Compound)

[0672] A liquid crystal polymer was synthesized, and it was confirmedthat the polymer was oriented in homeotropic alignment on a substratenot subjected to orienting treatment.

[0673] For synthesizing the polymer, 10 mmol of 4-n-heptyl benzoic acid,95 mmol of terephthalic acid, 50 mmol of methylhydroquinone diacetate,50 mmol of catechol diacetate and 100 mg of sodium acetate were used toperform polymerization at 270° C. for 12 hours under nitrogenatmosphere. The reaction product was dissolved in tetrachloroethane, andre-precipitated with methanol to obtain 22.0 g of liquid crystalpolyester. The prepared liquid crystal polyester had the logarithmicviscosity of 0.15, and formed a nematic phase as a liquid crystal phase.The phase transition temperature between the isotropic phase and theliquid crystal phase was observed at 240° C., and the glass transitionpoint was found at 75° C.

[0674] A 10 wt. % solution of the liquid crystal polyester dissolved ina mixed solvent of phenol/tetrachloroethane (6/4, by weight) wasprepared, and applied on a plate of soda glass according to the bar-coatmethod. After the solvent was removed, the applied polyester wassubjected to heat treatment at 190° C. for 30 minutes, and then left atroom temperature to cool and fix. As a result, an evenly oriented liquidcrystal film having the thickness of 15 μm was prepared. The film wasobserved through a conoscope, and thereby it was found that the liquidcrystal polymer had positive uniaxiality to form homeotropic alignment.

[0675] (Formation of Optically Anisotropic Layer)

[0676] An 8 wt. % tetrachloroethane solution of the liquid crystalpolyester was prepared, and applied on the above orientation layeraccording to the spin-coat method. After the solvent was removed, theapplied polyester was subjected to heat treatment at 190° C. for 20minutes, and then left at room temperature to cool and fix. Thethus-formed optical compensatory sheet (KH-A3) was transparent, and hadno aligning defect and an even thickness (1.55 μm).

COMPARATIVE EXAMPLE 10

[0677] The cellulose acetate solution used in Example 33 was directlyused as a dope, which cast on a band by means of a band casting machine.When the temperature of the dope on the band reached 40° C., the formedfilm was dried with air at 40° C. for 1 minute. After peeled from theband, the film was dried with air at 100° C. for 10 minutes, to preparea cellulose acetate film (thickness: 80 μm) in which the solventremained in the amount of 3.0 wt. %.

[0678] The optical characters of the prepared cellulose acetate film(CAF-H1) were measured. The results are set forth in Table 13. TABLE 13Retardation in- Film creasing agent Re550 Rth550 Example 33 CAF-01 3.5weight parts 8 nm 80 nm Example 34 CAF-02 2.5 weight parts 4 nm 90 nmExample 35 CAF-03 3.5 weight parts 9 nm 82 nm Comp. Ex. 10 CAF-H1 — 4 nm48 nm

EXAMPLE 36

[0679] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-A1)prepared in Example 33 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (CAF-01) might be on the polarizing membrane sideand so that the slow axis of the sheet (KH-A1) might be parallel to thetransmission axis of the membrane.

[0680] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 3.7

[0681] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-A2)prepared in Example 34 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (CAF-02) might be on the polarizing membrane sideand so that the slow axis of the sheet (KH-A2) might be parallel to thetransmission axis of the membrane.

[0682] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 38

[0683] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The optical compensatory sheet (KH-A3)prepared in Example 35 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thecellulose acetate film (CAF-03) might be on the polarizing membrane sideand so that the slow axis of the sheet (KH-A3) might be perpendicular tothe transmission axis of the membrane.

[0684] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

COMPARATIVE EXAMPLE 11

[0685] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The cellulose acetate film prepared inComparative Example 10 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that the slowaxis of the film (CAF-H1) might be perpendicular to the transmissionaxis of the membrane.

[0686] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

EXAMPLE 39

[0687] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 36 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet (KH-A1) might be on theliquid crystal cell side. The polarizing plates were arranged so thatthe transmission axes might be crossed perpendicularly.

[0688] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 14.

EXAMPLE 40

[0689] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 37 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet (KH-A2) might be on theliquid crystal cell side. The polarizing plates were arranged so thatthe transmission axes might be crossed perpendicularly.

[0690] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 14.

EXAMPLE 41

[0691] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 38 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet (KH-A3) might be on theliquid crystal cell side. The polarizing plates were arranged so thatthe transmission axes might be crossed perpendicularly.

[0692] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 14.

COMPARATIVE EXAMPLE 12

[0693] The viewing angle of the commercially available liquid crystaldisplay (6E-A3, Sharp Corporation), which has a liquid crystal cell ofTN mode, was measured by means of a measuring apparatus (EZ-Contrast160D, ELDIM) when each of eight tones of black (L1) to white (L8) wasdisplayed. The results are set forth in Table 14. TABLE 14 Viewingangle* LCD Upward Downward Left-rightward Example 39 70° 45° 160°Example 40 75° 45° 160° Example 41 30° 55° 120° Comp. Ex. 12 15° 25° 37°

EXAMPLE 42

[0694] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of 20 inches type (LC-20v1, SharpCorporation), which had a liquid crystal cell of TN mode. In place ofthe removed members, the polarizing plate prepared in Example 36 waslaminated on each side (each of the backlight side and the observerside) of the cell with an adhesive so that the optical compensatorysheet (KH-A1) might be on the liquid crystal cell side. The polarizingplates were arranged so that the transmission axes might be crossedperpendicularly.

[0695] The backlight of the prepared display had been kept on for 5hours under the conditions of 25° C. and 60% RH. After that, while ablack image was displayed on the whole screen, it was observed with theeyes in a dark room whether light leaked or not. As a result, it wasconfirmed that the display did not leak light.

EXAMPLE 43

[0696] The procedure of Example 42 was repeated except that thepolarizing plate prepared in Example 37 was used, and thereby it wasconfirmed that the display equipped with the polarizing plate of Example37 did not leak light.

EXAMPLE 44

[0697] The procedure of Example 42 was repeated except that thepolarizing plate prepared in Example 38 was used, and thereby it wasconfirmed that the display equipped with the polarizing plate of Example38 did not leak light.

COMPARATIVE EXAMPLE 13

[0698] The procedure of Example 42 was repeated except that thepolarizing plate prepared in Comparative Example 11 was used, andthereby it was confirmed that the display equipped with the polarizingplate of Comparative Example 11 leaked light at the peripheral area ofthe screen.

EXAMPLE 45

[0699] (Preparation of Optical Compensatory Sheet)

[0700] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0701] In another mixing tank, 16 weight parts of the retardationincreasing agent used in Example 1, 80 weight parts of methylenechloride and 20 weight parts of methanol were placed, heated andstirred, to prepare a retardation increasing agent solution.

[0702] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (25 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3.5 weight parts based on100 weight parts of cellulose acetate.

[0703] The prepared dope was cast on a band by means of a band castingmachine. After peeled from the band, the film was laterally stretched by25% at 130° C. with a tenter while the solvent remained in the amount of15 wt. %. The film was dried at 50° C. for 30 seconds with the widthkept with clips, to prepare a cellulose acetate film (opticalcompensatory sheet) having the thickness of 70 μm.

[0704] The Re and Rth retardation values (Re550 and Rth550) of theprepared cellulose acetate film (TAC-1) were measured at 550 nm by meansof an ellipsometer [M-150, JASCO], to find 40 nm and 130 nm,respectively.

[0705] (Saponification Treatment)

[0706] The obtained film (TAC-1) was immersed in a 1.5 N aqueous NaOHsolution (pH: 13) for 2 minutes (55° C.) to saponify, washed withflowing water and dried.

[0707] The Re retardation value (Re550) of the saponified film wasmeasured, and thereby the Re retardation difference (ΔRe=Re550 of thesaponified film−Re550 of the film before saponification) was obtained.Further, the concentration of eluted retardation increasing agent wasmeasured to determine the ratio of the eluted amount per the originalcontent of the retardation increasing agent. The results are set forthin Table 15.

COMPARATIVE EXAMPLE 14

[0708] (Preparation of Transparent Support)

[0709] The following components were placed in a mixing tank, heated andstirred to dissolve, to prepare a cellulose acetate solution. Celluloseacetate solution Cellulose acetate (acetic acid 100 weight partscontent: 60.9%) Triphenyl phosphate (plasticizer) 7.8 weight partsBiphenyldiphenyl phosphate 3.9 weight parts (plasticizer) Methylenechloride (first solvent) 300 weight parts Methanol (second solvent) 54weight parts 1-Butanol (third solvent) 11 weight parts

[0710] In another mixing tank, the following components were placed,heated and stirred to prepare to prepare a retardation increasing agentsolution. Components of retardation increasing agent solution2-Hydroxy-4-benzyloxybenzophenone 12 weight parts2,4-benzyloxybenzophenone  4 weight parts Methylene chloride 80 weightparts Methanol 20 weight parts

[0711] The cellulose acetate solution (474 weight parts) and theretardation increasing agent solution (22 weight parts) were mixed andstirred well to prepare a dope. The prepared dope contained theretardation increasing agent in the amount of 3 weight parts based on100 weight parts of cellulose acetate.

[0712] The dope was cast on a drum cooled at 0° C. The formed film waspeeled when the solvent content was 70 wt. %, and both sides of the filmwas fixed with a pin tenter. While the film was set up so that thestretching ratio might be 3% in the lateral direction (directionperpendicular to the machine), the film was dried until the solventcontent was 3 to 5 wt. %. The film was then transferred and dried in aheating apparatus equipped with many rollers. The stretching ratio alongthe tenter was essentially 0% at a temperature higher than 120° C.,which is the glass transition temperature. In order to stretch the filmalong the machine by 4% when the film was peeled, the stretching ratioin the direction perpendicular to the machine (in the lateral direction)was 0.75 times as much as the stretching ratio along the machine (in thelongitudinal direction). Thus, a cellulose acetate film having 107 μmthickness is produced.

[0713] The Re and Rth retardation values (Re550 and Rth550) of theprepared cellulose acetate film (TAC-3) were measured at 550 nm by meansof an ellipsometer [M-150, JASCO], to find 11 nm and 80 nm,respectively.

[0714] (Saponification Treatment)

[0715] The obtained film (TAC-3) was saponified in the same manner asExample 45.

[0716] The Re retardation difference (ΔRe=Re550 of the saponifiedfilm−Re550 of the film before saponification) and the concentration ofeluted retardation increasing agent (ratio of the eluted amount per theoriginal content of the retardation increasing agent) were measured. Theresults are set forth in Table 15. TABLE 15 Film ΔRe Eluted RI agent*Example 45 TAC-1 −2 nm 0.1% Comp. Ex. 14 TAC-3 −4 nm 0.7%

EXAMPLE 46

[0717] (Preparation of Polarizing Plate)

[0718] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The saponified optical compensatory sheet(TAC-1) prepared in Example 45 was then laminated on one surface of thepolarizing membrane with a polyvinyl alcohol adhesive so that thelongitudinal direction of TAC-1 might be parallel to that of thepolarizing membrane and so that the average direction of the slow axisof TAC-1 might be parallel to the transmission axis of the polarizingmembrane.

[0719] On the other surface of the membrane, a commercially availablecellulose triacetate film [Fujitac TD80UF, Fuji Photo Film Co., Ltd.]was saponified and laminated with a polyvinyl alcohol adhesive. Thus, apolarizing plate was prepared.

COMPARATIVE EXAMPLE 15

[0720] (Preparation of Polarizing Plate)

[0721] The procedure of Example 46 was repeated except that the notsaponified optical compensatory sheet (TAC-1) prepared in Example 45 wasused, to prepare a polarizing plate.

[0722] (Durability Test of Polarizing Plate)

[0723] Each of the polarizing plates prepared in Example 46 andComparative Example 15 was laminated on a glass plate with an acrylicadhesive, aged under the conditions of high temperature and elevatedpressure, and left in a thermostat at 90° C. for 1,000 hours. Thethus-treated plate was observed with the eyes to check whether thecellulose acetate film (optical compensatory sheet) was separated fromthe polarizing membrane or not, and whether bubbles were seen or not.The results are set forth in Table 16. TABLE 16 Separation*¹ Bubbles*²Example 46 Not separated Not seen Comp. Ex. 15 Separated Seen

[0724] (Viewing Angle Character of Polarizing Plate Attached on LiquidCrystal Cell of Vertical Alignment Mode)

[0725] A pair of polarizing plates and a pair of optical compensatorysheets were removed from a commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which has a liquid crystal cell comprisingvertically aligned liquid crystal molecules. In place of the removedmembers, the polarizing plate prepared in Example 46 was laminated oneach side (each of the backlight side and the observer side) of the cellwith an adhesive, so that the cellulose acetate film prepared in Example45 might be on the liquid crystal cell side. The polarizing plate on theobserver side was placed so that the transmission axis might be in theup-down direction, while the plate on the backlight side was placed sothat the transmission axis might be in the left-right direction. Thus,the polarizing plates were arranged in cross-Nicol position.

[0726] The viewing angle character of the obtained liquid crystaldisplay was measured by means of a measuring apparatus (EZ-Contrast160D, ELDIM), and thereby it was found that the angle range giving acontrast ratio of 10 or was 1600 or more (in up-down direction) or 160°or more (in left-right direction).

[0727] (Viewing Angle Character of Polarizing Plate Attached on LiquidCrystal Cell of TN Mode)

[0728] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display (6E-A3, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared in Example 46 was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive, so that the cellulose acetate film prepared in Example 45might be on the liquid crystal cell side. The polarizing plate on theobserver side was placed so that the transmission axis might be in theup-down direction, while the plate on the backlight side was placed sothat the transmission axis might be in the left-right direction. Thus,the polarizing plates were arranged in cross-Nicol position.

[0729] The viewing angle character of the obtained liquid crystaldisplay was measured by means of a measuring apparatus (EZ-Contrast160D, ELDIM), and thereby it was found that the angle range giving acontrast ratio of 10 without tone inversion was 45° (in up-downdirection) or 160° (in left-right direction).

EXAMPLE 47

[0730] (Preparation of Phase Retarder)

[0731] At room temperature, 120 weight parts of cellulose triacetate(average acetic acid content: 59.2%), 9.36 weight parts of triphenylphosphate, 4.68 weight parts of biphenyldiphenyl phosphate, 1.50 weightparts of the retardation increasing agent used in Example 1, 2.00 weightparts of tribenzylamine, 543.14 weight parts of methylene chloride,99.35 weight parts of methanol, and 19.87 weight parts of n-butanol weremixed to prepare a solution (dope).

[0732] The dope was cast on a band, dried at room temperature for 1minute, and further dried at 45° C. for 5 minutes. The formed film,which contained the remaining solvent in the amount of 30 wt. %, waspeeled from the band, dried at 120° C. for 10 minutes, and stretched at130° C. parallel to the casting direction while allowed to shrink freelyin the perpendicular direction. After stretched by 20%, the film wasdried at 120° C. for 30 minutes and then taken out. The obtained filmcontained the remaining solvent in the amount of 0.1 wt. %.

[0733] The formed cellulose acetate film (phase retarder) had thethickness of 54 μm, and its retardation values Re450, Re550 and Re590were measured at 450 nm, 550 nm and 590 nm by means of a measuringapparatus (EZ-Contrast 160D, ELDIM) to find 118.3 nm, 137.2 nm and 140.7nm, respectively. Accordingly, it was confirmed that the celluloseacetate film gave λ/4 in a wide wavelength region. Thus, a λ/4 plate wasobtained.

[0734] Further, the refractive index was measured by means of an Abbe'srefractometer and also the angular dependence of retardation wasmeasured at 550 nm, to determine the refractive index (nx) in thedirection parallel to the slow axis in the plane, the refractive index(ny) in the direction perpendicular to the slow axis in the plane, andthe refractive index (nz) in the thickness direction. From the obtainedrefractive indexes at 550 nm, the value of (nx−nz)/(nx−ny) wascalculated to find 1.58.

EXAMPLE 48

[0735] (Preparation of Retarder)

[0736] The dope prepared in Example 47 was cast by means of a bandcasting machine to form a film containing the remaining solvent in theamount of 15 wt. %. The film was laterally stretched with a tenter at150° C. by 45%.

[0737] The stretched cellulose acetate film (phase retarder) had thethickness of 40 μm, and its retardation values Re450, Re550 and Re590were measured at 450 nm, 550 nm and 590 nm by means of a measuringapparatus (EZ-Contrast 160D, ELDIM) to find 118.3 nm, 137.2 nm and 140.7nm, respectively. Accordingly, it was confirmed that the celluloseacetate film gave λ/4 in a wide wavelength region. Thus, a λ/4 plate wasobtained.

[0738] Further, the refractive index was measured by means of an Abbe'srefractometer and also the angular dependence of retardation wasmeasured at 550 nm, to determine the refractive index (nx) in thedirection parallel to the slow axis in the plane, the refractive index(ny) in the direction perpendicular to the slow axis in the plane, andthe refractive index (nz) in the thickness direction. From the obtainedrefractive indexes at 550 nm, the value of (nx−nz)/(nx−ny) wascalculated to find 1.70.

EXAMPLE 49

[0739] (Preparation of Phase Retarder)

[0740] At room temperature, 120 weight parts of cellulose triacetate(average acetic acid content: 59.0%), 2.0 weight parts of theretardation increasing agent used in Example 1, 9.36 weight parts oftriphenyl phosphate, 4.68 weight parts of biphenyldiphenyl phosphate,543.14 weight parts of methylene chloride, 99.35 weight parts ofmethanol and 19.87 weight parts of n-butanol were mixed to prepare asolution (dope).

[0741] The dope was cast on a band, dried at room temperature for 1minute, and further dried at 45° C. for 5 minutes. The formed film,which contained the remaining solvent in the amount of 30 wt. %, waspeeled from the band, dried at 120° C. for 5 minutes, and stretched at130° C. at the angle of 45° to the casting direction by about 50%. Afterdried at 130° C. for 20 minutes, the film was taken out. The obtainedfilm contained the remaining solvent in the amount of 0.1 wt. %.

[0742] The formed cellulose acetate film (phase retarder) had thethickness of 63 μm, and its retardation values Re450, Re550 and Re590were measured at 450 nm, 550 nm and 590 nm by means of a measuringapparatus (EZ-Contrast 160D, ELDIM) to find 115.7 nm, 137.4 nm and 141.1nm, respectively. Accordingly, it was confirmed that the celluloseacetate film gave λ/4 in a wide wavelength region. Thus, a λ/4 plate wasobtained. The Rth retardation value (Rth) was 137.5 nm.

[0743] Further, the refractive index was measured by means of an Abbe'srefractometer and also the angular dependence of retardation wasmeasured at 550 nm, to determine the refractive index (nx) in thedirection parallel to the slow axis in the plane, the refractive index(ny) in the direction perpendicular to the slow axis in the plane, andthe refractive index (nz) in the thickness direction. From the obtainedrefractive indexes at 550 nm, the value of (nx−nz)/(nx−ny) wascalculated to find 1.50.

EXAMPLE 50

[0744] (Preparation of Circularly Polarizing Plate)

[0745] The cellulose acetate film prepared in Example 47 and acommercially available polarizing plate (Sunritz Co., Ltd.) werelaminated with an adhesive so that the slow axis of the celluloseacetate film might be at the angle of 45° to the transmission axis ofthe polarizing plate, to prepare a circularly polarizing plate.

[0746] The obtained circularly polarizing plate gave almost completecircularly polarized light in a wide wavelength region (450 to 590 nm).

EXAMPLE 51

[0747] (Preparation of Polarizing Membrane)

[0748] Polyvinyl alcohol (average polymerization degree: 4,000,saponification degree: 99.8 mol. %) was dissolved in water to prepare4.0% aqueous solution. The solution was cast on a band, and dried toform a film. The film was then peeled off, stretched in the casingdirection, immersed for 1 minute in an aqueous solution containing 0.5g/l of iodine and 50 g/l of potassium iodine (liquid temperature: 30°C.), further immersed for 5 minutes in an aqueous solution containing100 g/l of boric acid and 60 g/l of potassium iodide (liquidtemperature: 70° C.), and washed in a water bath (temperature: 20° C.)for 10 seconds. The washed film was dried at 80° C. for 5 minutes toprepare a long polarizing membrane (width: 1,290 mm, thickness: 20 μm).

[0749] (Preparation of Circularly Polarizing Plate)

[0750] The cellulose acetate film prepared in Example 49, theabove-prepared polarizing membrane and a commercially availablecellulose triacetate film (Fujitac, Fuji Photo Film Co., Ltd.) werepiled up in this order and laminated through roll-to-roll, to prepare acircularly polarizing plate.

[0751] The obtained circularly polarizing plate gave almost completecircularly polarized light in a wide wavelength region (450 to 590 nm).

EXAMPLE 52

[0752] (Preparation of TN-Mode Liquid Crystal Display of ReflectionType)

[0753] A glass substrate having an ITO transparent electrode and anotherglass substrate having a finely rugged aluminum reflective electrodewere prepared. On the electrode of each glass substrate, a polyimideorientation layer (SE-7992, Nissan Chemicals Co., Ltd.) was formed andsubjected to rubbing treatment. The substrates were laminated so thatthe polyimide orientation layers might face to each other, and a spacerof 3.4 μm was inserted between the substrates. The substrates wereplaced so that the rubbing directions of the orientation layers might becrossed at the angle of 110°. To the gap between the substrates, aliquid crystal compound (MLC-6252, Merck) was injected to form a liquidcrystal layer. Thus, a liquid crystal cell of TN mode (twisted angle:70°, Δnd: 269 nm) was produced.

[0754] The λ/4 plate prepared in Example 47 was laminated with anadhesive on the glass substrate having the ITO transparent electrode,and further thereon a polarizing plate (a polarizing membrane laminatedwith a protective film whose surface was subjected to AR treatment) waslaminated.

[0755] To the thus-prepared liquid crystal display of reflection type,voltage of a square wave 1 kHz was applied. The display was thenobserved with eyes, and thereby it was confirmed that an image ofneutral gray was given without undesirable coloring in either white mode(1.5 V) or black mode (4.5 V).

[0756] The contrast ratio of reflection brightness was measured by meansof a meter (EZ-Contrast 160D, ELDIM), and thereby it was found that thefront contrast ratio was 25 and that the viewing angle giving thecontrast ratio of 3 was not less than 120° (up-downward) or not lessthan 120° (left-rightward). Further, the display was subjected to thedurability test (temperature: 60° C., relative humidity: 90%) for 500hours, but even so the displayed image had no defect.

EXAMPLE 53

[0757] (Preparation of STN-Mode Liquid Crystal Display of ReflectionType)

[0758] A glass substrate having an ITO transparent electrode and anotherglass substrate having a smooth aluminum reflective electrode wereprepared. On the electrode of each glass substrate, a polyimideorientation layer (SE-150, Nissan Chemicals Co., Ltd.) was formed andsubjected to rubbing treatment. The substrates were laminated so thatthe polyimide orientation layers might face to each other, and a spacerof 6.0 μm was inserted between the substrates. The substrates wereplaced so that the rubbing directions of the orientation layers might becrossed at the angle of 60°. To the gap between the substrates, a liquidcrystal compound (ZLI-2977, Merck) was injected to form a liquid crystallayer. Thus, a liquid crystal cell of STN mode (twisted angle: 240°,And: 791 nm) was produced.

[0759] A commercially available internal diffusing sheet (IDS, DaiNippon Printing Co., Ltd.) and the circularly polarizing plate preparedin Example 51 were laminated in this order with an adhesive on the glasssubstrate having the ITO transparent electrode, so the polarizing platemight be the top or bottom.

[0760] To the thus-prepared liquid crystal display of reflection type,voltage of a square wave 55 Hz was applied. The display was thenobserved with eyes, and thereby it was confirmed that an image ofneutral gray was given without undesirable coloring in either white mode(2.5 V) or black mode (2.0 V).

[0761] The contrast ratio of reflection brightness was measured by meansof a meter (EZ-Contrast 160D, ELDIM), and thereby it was found that thefront contrast ratio was 8 and that the viewing angle giving thecontrast ratio of 3 was 90° (up-downward) or 105° (left-rightward).

EXAMPLE 54

[0762] (Preparation of HAN-Mode Liquid Crystal Display of ReflectionType)

[0763] A glass substrate having an ITO transparent electrode and anotherglass substrate having a smooth aluminum reflective electrode wereprepared. On the ITO transparent electrode, a polyimide orientationlayer (SE-610, Nissan Chemicals Co., Ltd.) was formed and subjected torubbing treatment. On the aluminum reflective electrode, a verticalorientation layer (SE-1211, Nissan Chemicals Co., Ltd.) was formed andnot subjected to rubbing treatment. The substrates were laminated sothat the orientation layers might face to each other, and a spacer of4.0 μm was inserted between the substrates. To the gap between thesubstrates, a liquid crystal compound (ZLI-1565, Merck) was injected toform a liquid crystal layer. Thus, a liquid crystal cell of HAN mode(Δnd: 519 nm) was produced.

[0764] The λ/4 plate prepared in Example 47 was laminated with anadhesive on the glass substrate having the ITO transparent electrode,and further thereon a commercially available polarizing plate(NPF-G1225DU, Nitto Denko K.K.) was laminated. Furthermore, thereon alight-diffusing membrane (Lumisty, Sumitomo Chemical Co., Ltd.) waslaminated.

[0765] To the thus-prepared liquid crystal display of reflection type,voltage of a square wave 55 Hz was applied. The display was thenobserved with eyes, and thereby it was confirmed that an image ofneutral gray was given without undesirable coloring in either white mode(2.0 V) or black mode (0.8 V).

[0766] The contrast ratio of reflection brightness was measured by meansof a meter (EZ-Contrast 160D, ELDIM), and thereby it was found that thefront contrast ratio was 8 and that the viewing angle giving thecontrast ratio of 3 was not less than 120° (up-downward) or not lessthan 120° (left-rightward).

EXAMPLE 55

[0767] (Preparation of Liquid Crystal Display of G/H Type)

[0768] On a glass substrate having an ITO transparent electrode, apolymer for forming a vertical orientation layer (LQ-1800, Hitachi-DuPont Microsystems Co., Ltd.) was applied, dried and subjected to rubbingtreatment.

[0769] The λ/4 plate prepared in Example 48 was laminated with anadhesive on an aluminum-deposited glass substrate (reflection board). Onthe λ/4 plate, a SIO layer was formed with sputtering, and furtherthereon an ITO transparent electrode was provided. Furthermore, thereona solution of the polymer for forming a vertical orientation layer(LQ-1800, Hitachi-Du Pont Microsystems Co., Ltd.) was applied, dried andsubjected to rubbing treatment at the angle of 45° to the slow axis ofthe λ/4 plate.

[0770] The above-prepared two substrates were laminated so that theorientation layers might face to each other and so that the rubbingdirection of the orientation layers might be anti-parallel, and a spacerof 7.6 pm was inserted between the substrates. To the gap between thesubstrates, a mixture consisting of 2.0 wt. % of dichromatic dye(NKX-1366, Japan Photosensitive Dyes Co., Ltd.) and 98.0 wt. % of liquidcrystal compound (ZLI-2806, Merck) was injected according to the vacuuminjection method, to form a liquid crystal layer.

[0771] Voltage of a square wave 1 kHz was applied between the ITOelectrodes in the thus-prepared guest-host type liquid crystal displayof reflection type. The transmittances in white mode (1 V) or black mode(10 V) were measured to find 65% and 6%, respectively. Accordingly, theratio of transmittances (contrast ratio) between the image in white mode(1 V) and that in black mode (10 V) was 11:1. The viewing angle givingthe contrast ratio of 2:1 was measured to find 120° or more in bothdirections of up-down and left-right. The transmittances were alsomeasured while the voltage was changed, and thereby it was confirmedthat hysteresis did not appear in the transmittance-voltage curve.

COMPARATIVE EXAMPLE 16

[0772] (Preparation of λ/4 Plate)

[0773] Polycarbonate (weight average molecular weight: 100,000) wasdissolved in methylene chloride to prepare a 17 wt. % solution. Thesolution was cast on a glass plate to form a film (dry thickness: 80μm), dried at room temperature for 30 minutes, and further dried at 70°C. for 30 minutes. The formed polycarbonate film (evaporated amount:about 1 wt. %) was peeled from the glass plate, and cut into pieces(size: 5 cm×10 cm). One of the pieces was uniaxially stretched at 158°C. to prepare a stretched birefringent polycarbonate film.

[0774] The retardation values Re450, Re550 and Re590 of the formedpolycarbonate film (λ/4 plate) were measured at 450 nm, 550 nm and 590nm by means of an ellipsometer [M-150, JASCO], to find 147.8 nm, 137.5nm and 134.9 nm, respectively.

[0775] (Preparation of λ/2 Plate)

[0776] The above procedure was repeated except that the film was made tohave the dry thickness of 100 μm, to prepare a λ/2 plate.

[0777] The retardation values Re450, Re550 and Re590 of the formedpolycarbonate film (k/2 plate) were measured at 450 nm, 550 nm and 590nm by means of an ellipsometer [M-150, JASCO], to find 295.0 nm, 275.0nm and 269.8 nm, respectively.

[0778] (Preparation of TN-Mode Liquid Crystal Display of ReflectionType)

[0779] The above λ/4 plate, the above λ/2 plate and a polarizing plate(a polarizing membrane laminated with a protective film whose surfacewas subjected to AR treatment) were laminated in this order with anadhesive on the glass substrate with an ITO transparent electrode in theliquid crystal cell of TN-mode prepared in Example 52. They were placedso that the slow axis of the polarizing plate might be at the angle of20° to the slow axis of the λ/2 plate, and so that the slow axis of theλ/2 plate might be at the angle of 55° to the slow axis of the λ/4plate.

[0780] To the thus-prepared liquid crystal display of reflection type,voltage of a square wave 1 kHz was applied. The display was thenobserved with eyes, and thereby it was confirmed that the displayedimage was slightly yellowed in white mode (1.5 V) and slightly blued inblack mode (4.5 V).

[0781] The contrast ratio of reflection brightness was measured by meansof a meter (EZ-Contrast 160D, ELDIM), and thereby it was found that thefront contrast ratio was 10 and that the viewing angle giving thecontrast ratio of 3 was 100° (up-downward) or 80° (left-rightward).Further, the display was subjected to the durability test (temperature:60° C., relative humidity: 90% RH) for 500 hours, and as a result it wasobserved that the thus treated display gave a displayed image framedwith leaked light.

EXAMPLE 56

[0782] (Preparation of Cellulose Acetate Film SE5)

[0783] At room temperature, 45 weight parts of cellulose triacetate(average acetic acid content: 60.9%), 3.12 weight parts of the followingretardation increasing agent (4), 232.7 weight parts of methylenechloride, 42.57 weight parts of methanol, and 8.50 weight parts ofn-butanol were mixed to prepare a solution (dope).

[0784] Retardation Increasing Agent (4)

[0785] The obtained dope was cast by means of a band casting machine(effective length: 6 m), and dried to form a film SE5 (dry thickness: 60μm).

[0786] The retardation values Re550 and Rth550 of the formed celluloseacetate film SE5 were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to find 5 nm and 120 nm, respectively.

[0787] A gelatin undercoating layer of 0.1 μm thickness was formed onthe cellulose acetate film SE5, and thereon the coating solution fororientation layer used in Example 2 was applied in the amount of 28ml/m² by means of a wire bar coater of #16. The applied solution wasdried with hot air at 60° C. for 60 seconds, and then further dried withhot air at 90° C. for 150 seconds.

[0788] The formed layer was subjected to rubbing treatment in which therubbing direction was at the angle of 450 to the slow axis (measured at632.8 nm) of the cellulose acetate film SE5.

[0789] Independently, 41.01 g of the discotic (liquid crystal) compoundused in Example 2, 4.06 g of trimethylolpropane triacrylate denaturedwith ethylene oxide (V#360, Osaka Organic Chemicals Co., Ltd.), 0.90 gof cellulose acetate butyrate (CAB-551-0.2, Eastman Chemical), 0.23 g ofcellulose acetate butyrate (CAB-531-1, Eastman Chemical), 1.35 g of aphotopolymerization initiator (Irgacure 907, Ciba-Geigy) and 0.45 g of asensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) were dissolved in102 g of methyl ethyl ketone. The coating solution was then applied onthe above-formed orientation layer by means of a wire bar coater of #3.The thus-treated film was fixed on a metal frame, and heated in athermostat at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 130° C. for 4 secondswith ultraviolet rays emitted from a high pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optically anisotropic layer 1E was formed.

[0790] The Re retardation value (Re550) of the optically anisotropiclayer 1E was measured at 550 nm, and found 40 nm. The average angle(inclined angle) between the disc plane and the cellulose acetate filmSE was 42°.

[0791] (Preparation of Elliptically Polarizing Plate E)

[0792] The prepared cellulose acetate film SE5 was saponified in analkali bath, and was laminated with an adhesive on a polarizing membraneof polyvinyl alcohol and iodine, to prepare a polarizing plate. Further,the polarizing plate and the cellulose acetate film having the opticallyanisotropic layer 1E was laminated so that the SE5 face of the plate andthe cellulose acetate face (back face of the anisotropic layer 1E) mightbe in contact. The transmission axis of the polarizing membrane wasplaced perpendicularly to the slow axis of the cellulose acetate filmwith the anisotropic layer 1E (perpendicularly to the slow axis of thefilm SE5).

EXAMPLE 57

[0793] (Preparation of Cellulose Acetate Film SE6)

[0794] At room temperature, 45 weight parts of cellulose triacetate(average acetic acid content: 60.9%), 3.62 weight parts of the followingretardation increasing agent (1), 232.72 weight parts of methylenechloride, 42.57 weight parts of methanol, and 8.50 weight parts ofn-butanol were mixed to prepare a solution (dope).

[0795] Retardation Increasing Agent (1)

[0796] The obtained dope was cast by means of a band casting machine(effective length: 6 m), and stretched with a tenter to form a film SE6(dry thickness: 40 μm).

[0797] The retardation values Re550 and Rth550 of the formed celluloseacetate film SE6 were measured at 550 nm by means of an ellipsometer[M-150, JASCO], to find 18 nm and 100 nm, respectively.

[0798] The surface of the obtained film SE6 was saponified with a 2 Naqueous NaOH solution, and washed with water. The contact angle of thesaponified surface with pure water was 30°.

[0799] On the saponified surface, the coating solution for orientationlayer used in Example 2 was applied in the amount of 28 ml/m² by meansof a wire bar coater of #16. The applied solution was dried with hot airat 60° C. for 60 seconds, and then further dried with hot air at 90° C.for 150 seconds.

[0800] The formed layer was subjected to rubbing treatment in which therubbing direction was at the angle of 45° to the slow axis (measured at632.8 nm) of the cellulose acetate film SE6.

[0801] Independently, 41.01 g of the discotic (liquid crystal) compoundused in Example 2, 4.06 g of trimethylolpropane triacrylate denaturedwith ethylene oxide (V#360, Osaka Organic Chemicals Co., Ltd.), 0.90 gof cellulose acetate butyrate (CAB-551-0.2, Eastman Chemical), Q.23 g ofcellulose acetate butyrate (CAB-531-1, Eastman Chemical), 1.35 g of aphotopolymerization initiator (Irgacure 907, Ciba-Geigy) and 0.45 g of asensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) were dissolved in102 g of methyl ethyl ketone. The coating solution was then applied onthe above-formed orientation layer by means of a wire bar coater of #3.The thus-treated film was fixed on a metal frame, and heated in athermostat at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 130° C. for 4 secondswith ultraviolet rays emitted from a high pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optically anisotropic layer 1F was formed.

[0802] The Re retardation value (Re550) of the optically anisotropiclayer 1F was measured at 550 nm, and found 40 nm. The average angle(inclined angle) between the disc plane and the cellulose acetate filmSE was 42°.

[0803] (Preparation of Elliptically Polarizing Plate F)

[0804] The prepared cellulose acetate film SE6 was saponified in analkali bath, and was laminated with an adhesive on a polarizing membraneof polyvinyl alcohol and iodine, to prepare a polarizing plate. Further,the polarizing plate and the cellulose acetate film having the opticallyanisotropic layer 1F was laminated so that the SE6 face of the plate andthe cellulose acetate face might be in contact. The transmission axis ofthe polarizing membrane was placed parallel to the slow axis of thecellulose acetate film with the anisotropic layer iF (parallel to theslow axis of the film SE6).

COMPARATIVE EXAMPLE 17

[0805] (Preparation of Cellulose Acetate Film SE7)

[0806] On a commercially available cellulose triacetate film (FujitacTD80UF, Fuji Photo Film Co., Ltd.) having 100 μm thickness, a gelatinundercoating layer of 0.1 μm thickness was provided to prepare acellulose acetate film SE7.

[0807] The retardation values (Re550 and Rth550) were measured at 550 nmto find 0.6 nm and 35 nm, respectively.

[0808] On the gelatin undercoating layer of SE7, the coating solutionfor orientation layer used in Example 2 was applied in the amount of 28ml/m² by means of a wire bar coater of #16. The applied solution wasdried with hot air at 60° C. for 60 seconds, and then further dried withhot air at 90° C. for 150 seconds.

[0809] The formed layer was subjected to rubbing treatment in which therubbing direction was at the angle of 450 to the slow axis (measured at632.8 nm) of the cellulose acetate film.

[0810] Independently, 41.01 g of the discotic (liquid crystal) compoundused in Example 2, 4.06 g of trimethylolpropane triacrylate denaturedwith ethylene oxide (V#360, Osaka Organic Chemicals Co., Ltd.), 0.90 gof cellulose acetate butyrate (CAB-551-0.2, Eastman Chemical), 0.23 g ofcellulose acetate butyrate (CAB-531-1, Eastman Chemical), 1.35 g of aphotopolymerization initiator (Irgacure 907, Ciba-Geigy) and 0.45 g of asensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) were dissolved in102 g of methyl ethyl ketone. The coating solution was then applied onthe above-formed orientation layer by means of a wire bar coater of #3.The thus-treated film was fixed on a metal frame, and heated in athermostat at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 130° C. for 1 minutewith ultraviolet rays emitted from a high pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optically anisotropic layer 1G was formed.

[0811] The Re retardation value (Re550) of the optically anisotropiclayer 1G was measured at 550 nm, and found 40 nm. The average angle(inclined angle) between the disc plane and the cellulose acetate filmSE7 was 42°.

[0812] Resin of 2,2′-bis(4-hydroxyphenyl)propane polycarbonate(viscosity average molecular weight: 28,000) was dissolved indichloromethane to prepare 18 wt. % solution. The solution was defoamedin vacuo to prepare a dope. The dope was cast on a band, and dried at50° C. for 10 minutes, and the formed film was peeled and further driedat 100° C. for 10 minutes. The film was then longitudinally stretched at170° C. by 3.3%, and laterally stretched by 4.7% to obtain a biaxiallystretched film of 80 μm thickness in the form of roll. The longitudinalstretching was controlled with a pair of checking rollers differentiallyrotating, and the lateral stretching was controlled with width of thetenter.

[0813] The retardation values (Re550 and Rth550) were measured at 550 nmto find 4 nm and 205 nm, respectively.

[0814] (Preparation of Elliptically Polarizing Plate G)

[0815] The prepared polycarbonate film was laminated with an adhesive ona polarizing membrane of polyvinyl alcohol and iodine, to prepare apolarizing plate. Further, the polarizing plate and the celluloseacetate film having the optically anisotropic layer 1G was laminated sothat the polycarbonate face of the plate and the cellulose acetate SE7face might be in contact, to prepare an elliptically polarizing plate G.The transmission axis of the polarizing membrane was placedperpendicularly to the slow axis of the cellulose acetate film with theanisotropic layer 1G (perpendicularly to the slow axis of thepolycarbonate film).

[0816] (Optical Characters of Elliptically Polarizing Plates)

[0817] The optical characters of the elliptically polarizing platesprepared in Examples 56, 57 and Comparative Example 17 are set forth inTable 17. TABLE 17 First optical Second optical anisotropic layeranisotropic layer Re550*¹ β*³ Re550*¹ Rth550*² Example 56 40 nm 42° 12.0nm 250 nm Example 57 40 nm 42° 40.0 nm 210 nm Comp. 17 40 nm 42°  3.6 nm235 nm

EXAMPLE 58

[0818] (Preparation of Liquid Crystal Cell of Bend Alignment Mode)

[0819] On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having Δn of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment.

[0820] While voltage (5 or 5.5 V) of a square wave 55 Hz was applied tothe prepared liquid crystal cell of bend alignment mode, the Reretardation values were measured at 436 nm, 546 nm and 611.5 nm.

[0821] (Preparation of Liquid Crystal Display)

[0822] Two elliptically polarizing plates E prepared in Example 56 werelaminated on the prepared liquid crystal cell of bend alignment mode sothat the cell might be between the plates. The plates were arranged sothat the optically anisotropic layer in each plate might face to thecell substrate and so that the rubbing directions of the cell and theoptically anisotropic layer might be anti-parallel.

EXAMPLE 59

[0823] (Preparation of Liquid Crystal Display)

[0824] Two elliptically polarizing plates F prepared in Example 57 werelaminated on the liquid crystal cell of bend alignment mode prepared inExample 58 so that the cell might be between the plates. The plates werearranged so that the optically anisotropic layer in each plate mightface to the cell substrate and so that the rubbing directions of thecell and the optically anisotropic layer might be anti-parallel.

COMPARATIVE EXAMPLE 18

[0825] (Preparation of Liquid Crystal Display)

[0826] Two elliptically polarizing plates G prepared in ComparativeExample 17 were laminated on the liquid crystal cell of bend alignmentmode prepared in Example 58 so that the cell might be between theplates. The plates were arranged so that the optically anisotropic layerin each plate might face to the cell substrate and so that the rubbingdirections of the cell and the optically anisotropic layer might beanti-parallel.

[0827] (Evaluation of Liquid Crystal Display)

[0828] Voltage of a square wave 55 Hz was applied to the liquid crystalcell of each of the liquid crystal displays prepared in Examples 58, 59and Comparative Example 18. An image was displayed according to normallywhite mode (white: 2V, black: 5V). The viewing angle giving the contrastratio (transmittance ratio of white display/black display) of 10 wasmeasured in both up-down and left-right directions.

[0829] Further, after the backlight was kept on for 2 hours, a blackimage was displayed and its image quality was observed. TABLE 18 Viewingangle Up Down Left Right Image quality Example 58 80° 73° 59° 57° GoodExample 59 80° 75° 78° 78° Good Comp. Ex. 18 80° 58° 56° 55° Lightleaked*

1. An optical compensatory sheet comprising a cellulose acetate filmwhich contains 100 weight parts of cellulose acetate having an aceticacid content of 59.0 to 61.5%, and 0.01 to 20 weight parts of anaromatic compound having at least two aromatic rings, wherein thecellulose acetate film has an Re retardation value measured at 550 nm(Re550) in the range of 0 to 200 nm, an Rth retardation value measuredat 550 nm (Rth550) in the range of 70 to 400 nm, and a thickness in therange of 10 to 70 μm.
 2. The optical compensatory sheet as defined inclaim 1, wherein the Re550 value is in the range of 20 to 70 nm.
 3. Theoptical compensatory sheet as defined in claim 1, wherein the celluloseacetate film has an Re retardation value measured at 450 nm (Re450) inthe range of 100 to 125 nm and an Re retardation value measured at 590nm (Re590) in the range of 120 to 160 nm, said Re450 and Re590 valuessatisfying the condition of Re590−Re450≧2 nm.
 4. The opticalcompensatory sheet as defined in claim 1, wherein the cellulose acetatefilm is subjected to a saponification treatment, and the saponificationtreatment changes the Re550 value by 3 nm or less.
 5. The opticalcompensatory sheet as defined in claim 1, wherein the cellulose acetatefilm has at least one surface having a surface energy of 55 to 75 mN/m.6. The optical compensatory sheet as defined in claim 1, wherein thecellulose acetate film has at least one surface subjected to a coronadischarge treatment at a discharge frequency of 50 Hz to 5,000 kHz. 7.The optical compensatory sheet as defined in claim 1, wherein thecellulose acetate film has at least one surface saponified with analkaline solution of a concentration in the range of 0.1 to 3.0 N. 8.The optical compensatory sheet as defined in claim 1, wherein thecellulose acetate film is subjected to a stretching treatment.
 9. Theoptical compensatory sheet as defined in claim 8, wherein the stretchingtreatment is conducted at a stretching ratio in the range of 3 to 100%.10. The optical compensatory sheet as defined in claim 8, wherein thecellulose acetate film is biaxially stretched.
 11. The opticalcompensatory sheet as defined in claim 1, wherein the Re550 value is inthe range of 0 to 20 nm.
 12. The optical compensatory sheet as definedin claim 11, wherein an optically anisotropic layer is formed from aliquid crystal compound.on the cellulose acetate film.
 13. The opticalcompensatory sheet as defined in claim 12, wherein the liquid crystalcompound is a discotic compound.
 14. The optical compensatory sheet asdefined in claim 1, wherein the aromatic compound has at least one1,3,5-triazine ring.
 15. A polarizing plate which comprises a pair oftransparent protective films and a polarizing membrane provided betweenthe films, one of said transparent protective films comprising acellulose acetate film which contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,wherein the cellulose acetate film has an Re retardation value measuredat 550 nm (Re550) in the range of 0 to 200 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm, and athickness in the range of 10 to 70 μm.
 16. A liquid crystal displaycomprising a pair of polarizing plates and a liquid crystal cellprovided between the plates, wherein each of the polarizing platescomprises a pair of transparent protective films and a polarizingmembrane provided between the films, at least one of said transparentprotective films placed between the cell and the membranes comprising acellulose acetate film which contains 100 weight parts of celluloseacetate having an acetic acid content of 59.0 to 61.5% and 0.01 to 20weight parts of an aromatic compound having at least two aromatic rings,wherein the cellulose acetate film has an Re retardation value measuredat 550 nm (Re550) in the range of 0 to 200 nm, an Rth retardation valuemeasured at 550 nm (Rth550) in the range of 70 to 400 nm, and athickness in the range of 10 to 70 μm.
 17. The liquid crystal display asdefined in claim 16, wherein the liquid crystal cell works according toTN mode, VA mode, MVA mode, n-ASM mode or OCB mode.
 18. A circularlypolarizing plate which comprises an optical compensatory sheet and alinearly polarizing membrane, said compensatory sheet and said linearlypolarizing membrane being so arranged that a slow axis in plane of thecompensatory sheet is oriented essentially at an angle of 45° to atransmission axis of the linearly polarizing plate, said opticalcompensatory sheet comprising a cellulose acetate film which contains100 weight parts of cellulose acetate having an acetic acid content of59.0 to 61.5% and 0.01 to 20 weight parts of an aromatic compound havingat least two aromatic rings, wherein the cellulose acetate film has anRe retardation value measured at 550 nm (Re550) in the range of 0 to 200nm, an Rth retardation value measured at 550 nm (Rth550) in the range of70 to 400 nm, a thickness in the range of 10 to 70 μm, an Re retardationvalue measured at 450 nm (Re450) in the range of 100 to 125 nm, and anRe retardation value measured at 590 nm (Re590) in the range of 120 to160 nm, said Re450 and Re590 values satisfying the condition ofRe590−Re450≧2 nm.
 19. A liquid crystal display of a reflection typecomprising a reflection board, a liquid crystal cell and a polarizingmembrane in this order, and a cellulose acetate film being providedbetween said reflection board and said polarizing membrane, wherein thecellulose acetate film contains 100 weight parts of cellulose acetatehaving an acetic acid content of 59.0 to 61.5% and 0.01 to 20 weightparts of an aromatic compound having at least two aromatic rings, saidcellulose acetate film having an Re retardation value measured at 550 nm(Re550) in the range of 0 to 200 nm, an Rth retardation value measuredat 550 nm (Rth550) in the range of 70 to 400 nm, a thickness in therange of 10 to 70 μm, an Re retardation value measured at 450 nm (Re450)in the range of 100 to 125 nm, and an Re retardation value measured at590 nm (Re590) in the range of 120 to 160 nm, said Re450 and Re590values satisfying the condition of Re590−Re450≧2 nm.
 20. A liquidcrystal display comprising a pair of polarizing plates and a liquidcrystal cell of bend alignment mode provided between the plates, whereinat least one polarizing plate is an elliptically polarizing plate whichcomprises a first optically anisotropic layer comprising discoticmolecules oriented in hybrid alignment, a second optically anisotropiclayer comprising at least one cellulose acetate film, and a polarizingmembrane, said polarizing membrane being arranged as an outermost layer,said first and second optically anisotropic layers and said polarizingmembrane being so arranged that a direction giving the maximumrefractive index in plane of the first optically anisotropic layer isoriented essentially at an angle of 45° to a transmission axis in planeof the polarizing membrane and that a direction giving the maximumrefractive index in plane of the second optically anisotropic layer isdirected essentially parallel or perpendicular to a transmission axis inplane of the polarizing membrane, wherein the cellulose acetate film ofthe second optically anisotropic layer contains 100 weight parts ofcellulose acetate having an acetic acid content of 59.0 to 61.5% and0.01 to 20 weight parts of an aromatic compound having at least twoaromatic rings, said cellulose acetate film having an Re retardationvalue measured at 550 nm (Re550) in the range of 1 to 20 nm, an Rthretardation value measured at 550 nm (Rth550) in the range of 150 to 300nm, and a thickness in the range of 10 to 70 μm.
 21. A liquid crystaldisplay comprising a pair of polarizing plates and a liquid crystal cellof bend alignment mode provided between the plates, wherein at least onepolarizing plate is an elliptically polarizing plate which comprises afirst optically anisotropic layer comprising discotic molecules orientedin hybrid alignment, a second optically anisotropic layer comprising atleast one cellulose acetate film, and a polarizing membrane, saidpolarizing membrane being arranged as an outermost layer, said first andsecond optically anisotropic layers and said polarizing membrane beingso arranged that a direction giving the maximum refractive index inplane of the first optically anisotropic layer is oriented essentiallyat an angle of 45° to a transmission axis in plane of the polarizingmembrane and that a direction giving the maximum refractive index inplane of the second optically anisotropic layer is directed essentiallyparallel to a transmission axis in plane of the polarizing membrane,wherein the cellulose acetate film of the second optically anisotropiclayer contains 100 weight parts of cellulose acetate having an aceticacid content of 59.0 to 61.5% and 0.01 to 20 weight parts of an aromaticcompound having at least two aromatic rings, said cellulose acetate filmhaving an Re retardation value measured at 550 nm (Re550) in the rangeof 20 to 100 nm, an Rth retardation value measured at 550 nm (Rth550) inthe range of 150 to 300 nm, and a thickness in the range of 10 to 70 μm.